Bell 
EL  Dorado,  Arkansas  oil  and  gas  field* 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


The  RALPH  D.  REED  LIBRARY 

O 

DEPARTMENT  OF  GEOLOGY 

UNIVERSITY  OF  CALIFORNIA 

LOS  ANGELES,  CALIF. 


STATE  OF  ARKANSAS 

Bureau  of  Mines,  Manufactures  and  Agriculture 
JIM  G.  FERGUSON,  Commissioner 


The 

El  Dorado,  Arkansas 
Oil  and  Gas  Field 


Geological  Outline 

Operation  Methods 

Conservation 


By 

H.  W.  Bell  and  J.  B.  Kerr  of 
the  U.  S.  Bureau  of  Mines 


Published  Under  the 
Joint  Auspices  of  the 


UNITED  STATES  BUREAU  OF  MINES,  THE  UNITED  STATES  GEOLOGI- 
CAL   SURVEY,    THE    UNIVERSITY    OF    ARKANSAS    AND 
THE  STATE  BUREAU  OF  MINES,  MANUFAC- 
TURES AND  AGRICULTURE 

LITTLE      ROCK,     ARKANSAS 
1922 


CONTENTS 


PART  I 
U.  S.  BUREAU  OF  MINES 

Page 

Introduction  7 

Acknowledgments    . 7 

History  of  Development 8 

First  Wells , 8 

Acreage  and  Oil  Prices 11 

Storage  and  Marketing  Facilities 11 

State  Conservation  Commission 12 

Co-operation  by  U.  S.  Bureau  of  Mines 12 

Drilling   Methods 13 

Equipment  arid  Power 13 

Casing  Program 14 

Testing   Formations 14 

Completing  Wells 18 

Labor  Conditions 20 

Drilling   Costs 22 

Water  Conditions 22 

Amount  Water  Produced 22 

Harmful  Effects  of  Water 22 

Source   of  Water 23 

Analyses  of  Underground  Waters  in  El  Dorado  Field 31 

Association  of  Oil  and   Water 33 

Use  of  Cement 34 

Handling  of  Cement 40 

Abandonment  of  Wells 41 

Protection  in  Case  of  Deeper  Production 43 

Production  Record 44 

Oil  Produced,  Proven  Acreage,   Well   Spacing 44 

Quality  of  Oil 48 

Surface   Wastage 48 

Production  of  Gas 51 

Production  Decline  Curves  for  Oil  Wells 53 

Production  Methods 1 55 

Safety  Devices 56 

Oil,  Gas  and  Water  Separators 58 

Dehydration  60 

Natural  Gas  Gasoline 62 

Types  of  Oil  Well  Pumps 64 

Oil  Recovery  from  Unconsolidated  Sands 64 

Perforated  Liners  and  Screen  Pipe 65 

Flow  Oil  through  Tubing 66 

Air  Lifts  for  Raising  Oil 66 

Vacuum  Pumping 67 

Power  for  Pumping 67 

Counterbalances  and  Tail  Pumps 68 

Conclusion    ...  Kg 


Librarj 
TN 


CONTENTS 


ILLUSTRATIONS 

Page 

Frontispiece.    Airplane  View  of  El  Dorado  Oil  Field 6 

Plate          A.     Map  of  El  Dorado  Oil  Field Pocket 

Plate  I.     Busey  Well    (shown   in  foreground),   Section   31-17-15, 

the  first  oil  well  completed  in  the  El  Dorado  Field. 
Well  began  producing  January  10,  1921.     Photo  taken 

after  abandonment  of  well 9 

Plate          II.     Bailing  down  to  bring  in  well.     Connections  made  for 

Flowing  Well  17 

Plate  III.  Water  Infiltration  Possibilities  and  Method  of  Cement- 
ing Bottom  of  Hole  under  Pressure...... Pocket 

Plate  IV.  Generalized  Sections,  Showing  Approximate  Thick- 
ness of  Oil-Bearing  Strata  and  Association  of  Oil  and 

Water Pocket 

Plate          V.     Diagrammatic    Northeasternly    Cross    Section   in   Nor-  , 

them  Part  of  El  Dorado  Oil  Field Pocket 

Plate         VI.     Diagrammatic    Easterly    Cross    Section    in    Southern 

Part  of  El  Dorado  Field Pocket 

Plate  VII.  North-South  Diagrammatic  Composite  Section,  Show- 
ing Character  of  Strata  Comprising  the  Oil  Zone  and 

adjacent  to  it '. Pocket 

Plate  VIII.  Preparing  to  Cement  Well  under  Pressure  in  Bottom. 
Arkansas  Natural  Gas  Co.,  Wood  No.  199,  Section 

20-18-15 38 

Plate         IX.     Intensive  Drilling  near  South  Boundary  of  Section  17- 

18-15.     Shows  Open  Earthen  Sump  for  Oil  Storage 45 

Plate          X.     Estimated  Oil  Production  of  Average  Wells  of  Field..  Pocket 

Plate         XI.     Waste  of  Oil  by  Storage  in  Earthen  Sump 50 

Plate  XII.  A  55,000-barrel  Steel  Tank  on  the  Standard  Oil  Tank 
Farm.  Shows  Portion  of  Adequate  Fire  Wall  which 

Centers  the  Tank  in  a  Closed  Basin 51 

Plate      XIII.     Average  Production  Decline  Curve Pocket 

Plate     XIV.     A  Steel  Choke  Worn  by  Passage  of  Sand  with  Oil 55 

Plate       XV.     "Christmas  Tree"  Equipment  of  about  Average  Design  56 

Plate  XVI.  Discharge  of  Water  and  Some  Oil  from  Separator. 
Gas  and  Oil  Risers  at  Ends  of  Separator  not  Shown, 
Some  Oil  being  Wasted  with  the  Water  through  the 

Bleeders  59 

Plate    XVII.     Discharge  of  Water  from  Separator,  Clear  Water  being 

Discharged  from  the  Bleeders.. 59 

Plate  VXIII.     The  Two-Unit  Electric  Dehydrator  on  the  Hearin  Lease 

of  the   Humble  Oil  Company 61 

FIGURES 

Fig.  1.  Cable  Tool  Lubricator  for  High  Pressure  Wells 21 

Fig.  2.  Dump   Bailer 37 

Fig.  3.  Field   Production   Curves Pocket 

Fig.  4.  Gas-Oil-Water  Separator 57 

Fig.  5.  Sand  Trap  Used  in  Some  of  the  Pumping  Weils 63 

TABLES 

Table  1.  Production,    Deliveries,    and    Stocks    of    Oil,    and    Dry 

Holes,  and  Gas  Wells  of  El  Dorado  Oil  Field,  January 

to  October,   1921 10 

Table  2.  Collapsing  Pressure  and  Capacities Pocket 

Table  3.  Table  of  Capacities  between  Casing  of  Different  Sizes 

and  Weights 15 

Table  4.  Water  Analyses  of  El  Dorado  Field 65 

Table  5  Analysis  of  El  Dorado,  Arkansas,  Crude  Oil 49 

Table  6.  Decline  in  Gas  Pressure  and  Production  of   Some  of 

the  Wells  of  El  Dorado. 52 

Table  7.  Estimated  Future  and  Ultimate  Production  for  an  Av- 
erage Well  in  the  El  Dorado  Field 53 


76309O 


CONTENTS 


PART  II 

U.  S.  GEOLOGICAL  SURVEY 
El  Dorado  Oil  Field—  Page 

Discovery   and   Development 71 

Studies  of  the  Geology 71 

Structure  of  the  Field 71 

How  the  Pool  Was  Formed 74 

Oil  and  Gas  above  the  Principal  "Pay"  Sand 75 

Possible  Extension  of  the  Field 75 

Possibilities  of  Similar  Fields  Elsewhere  in  Southern  Arkansas 75 

Description  of   Producing  Beds 76 

Methods  Used  in   Constructing  the  Map 76 

Character  of  the   Oil 77 

Some   Mistakes  in   Drilling  Methods 79 

Elevations  of  Nacatoch  Sands 78 

Ages,    Relative   Positions   and    Thickness   of   Formations    Encoun- 
tered in  Drilling  in  the  El  Dorado  Field 79 

Yegua  ( ?)  Formation 79 

St.   Maurice   Formation 79 

Wilcox   Formation 80 

Midway  Formation  80 

Arkadelphian   Clay 80 

Nacatoch  Sand 80 

Marlbrook  Marl 80 

Annona  Tongue  of  the  Austin  Chalk   (?) 81 

Brownstown  Marl 81 

Blossom   ( ?)   Sand 81 

Eagle  Ford   (?)    Clay 81 

Record  of  Deep  aWell  Near  El  Dorado 

Geologic  Structure  in  the  Region 


MAPS 

Structure  of  Northern  Part  of  El  Dorado  Field 72 

Cross  Section  of  Southern  Arkansas Pocket 

PART  III 

DATA  BY  J.  A.  BRAKE, 
State  Oil  and  Gas  Inspector 

Extensions  of  El  Dorado  Field  north,  east  and  west 87 

Log  of  Murphy  No.  1  Well 87 

Log  of  Frazier  Well 89 

ILLUSTRATIONS 
Burning  Well  by  Day  and  by  Night 88-90 


Fo 


rewor 


IN  THE  absence  of  a  State  Geological  Survey,  and  without  an  appropria- 
tion of  any  kind  for  research  work,  the  Bureau  of  Mines,  Manufactures 
and  Agriculture  is  fortunate  in  being  able  to  give  to  the  public  this  re- 
port on  the  petroleum  and  natural  gas  resources  of  the  El  Dorado  field, 
together  with  the  timely  recommendations  embraced  therein  for  the  guid- 
ance  of   drilling   operations   and   for   the   conservation   of   these   important 
minerals. 

Publication  of  this  material  has  been  made  possible  by  a  prompt  and 
cordial  response  to  the  State's  call  for  co-operation  upon  the  United  States 
Bureau  of  Mines  and  by  substantial  aid  from  the  University  of  Arkansas 
and  the  State  Banking  Department.  The  report  also  includes  timely  data 
on  the  geological  features  of  the  field  previously  issued  in  press  bulletins 
by  the  United  States  Geological  Survey. 

It  has  been  difficult  to  work  out  some  of  the  problems  met  with,  both 
in  a  study  of  the  geology  of  the  region  and  in  the  methods  of  drilling  and 
controlling  the  wells,  and  the  report  has  been  delayed  to  await  the  settle- 
ment of  some  of  these  perplexing  questions.  It  has  been  especially  difficult 
to  correlate  the  well  logs,  necessary  to  a  correct  understanding  of  the  struc- 
ture, due  chiefly  to  the  use  of  rotary  equipment,  which  gives  up  few  fossils. 
The  report  was  held  up  some  three  months  awaiting  the  geologic  matter. 

With  this  explanation,  I  am  pleased  to  give  the  public  the  report  as 
furnished  by  the  co-operating  agencies  of  the  Federal  Government,  without 
change.  The  expense  of  publication  is  defrayed  wholly  by  this  depart- 
ment, out  of  its  limited  printing  fund.  A  copy  of  the  report  may  be  obtained 
free  by  any  citizen  of  Arkansas  or  person  residing  outside  of  the  state  who 
is  actually  interested  in  oil  and  gas  development. 


Commissioner  of  Mines,  Manufactures  and  Agriculture. 
JOHN  C.  SMALL, 

Editor  of  Publications. 


Drilling  and  Production 

H.  W.  BELL*  AND  J.  B.  KERRf 

The  United  States  Geological  Survey  has  compiled  a  report  dealing 
with  the  geologic  features,  the  accumulation  of  oil  and  gas  and  the  possi- 
bilities of  extending  the  producing  area  of  the  El  Dorado  Oil  Field,  Arkan- 
sas. The  engineers  of  the  Bureau  of  Mines  have  made  a  study  and  prepared 
the  following  data  on  methods  of  drilling  and  production.  It  is  believed 
that  if  some  of  the  suggestions  in  this  report  are  adopted,  the  operator  will 
enjoy  a  greater  profit.  These  suggestions  are  primarily  based  upon  the  prin- 
ciples of  the  conservation  of  oil  and  gas. 

The  El  Dorado  Oil  Field,  Arkansas,  has  developed  rapidly  since  January 
10,  1921,  when  the  first  well  that  produced  commercial  quantities  of  oil  was 
completed.  The  low  prices  for  oil  and  lack  of  adequate  pipe  lines  and  tank- 
age in  the  earlier  months,  did  not  apparently  retard  the  rate  of  development 
to  any  extent.  Up  to  November  1,  1921,  the  field  had  produced  approx- 
imately 10,000,000  barrels  of  oil  from  a  proven  oil  area  of  about  4,825  acres, 
which  was  an  average  of  2,150  barrels  to  the  acre. 

The  maximum  daily  production  of  the  field  was  about  77,000  barrels, 
which  occurred  for  a  few  days  in  August,  1921.  The  production  decreased 
to  about  44,000  barrels  per  day  by  the  middle  of  October,  1921.  Since 
August,  1921,  producing  wells  were  completed  at  the  average  rate  of  about 
twenty  per  week  for  three  months.  By  the  end  of  October,  1921,  about  460 
commercial  oil  wells  had  been  completed.  The  initial  productions  of  the 
oil  wells  ranged  from  only  a  few  barrels  to  15,000  barrels  of  oil  per  day  and 
the  gas  wells  up  to  a  maximum  of  about  40,000,000  cubic  feet  of  gas  per 
day.  Unfortunately,  some  of  the  wells  have  'been  inefficiently  handled, 
which  has  resulted  in  considerable  waste. 

The  El  Dorado  field  furnished  the  first  commercial  production  of  oil 
in  the  State  of  Arkansas.  Gas  has  been  produced  since  about  1905  in  the 
Fort  Smith  gas  field,  which  lies  near  the  Oklahoma  line  and  some  175  miles 
northwest  of  El  Dorado.  Because  of  this  gas  production,  the  Arkansas  Leg- 
islature passed  an  Act  in  1917  which  dealt  with  the  conservation  of  oil  and 
gas.  The  situation  for  El  Dorado  was  therefore  unique,  in  that  the  first 
oil  production  of  the  State  was  immediately  subject  to  the  regulations  of 
a  conservation  commission. 

The  excessive  production  of  sand  with  the  oil  has  been  the  source  of 
much  trouble  to  the  operators  and  has  caused  them  to  give  considerable 
attention  to  the  handling  of  this  problem. 

The  excessive  production  of  water  in  some  areas  has  curtailed  or 
stopped  the  production  of  oil  and  gas.  Several  factors  have  contributed  to 
a  more  rapid  increase  in  water  production  than  was  necessary.  One  object 
of  this"  report  is  to  indicate  the  harmful  effect  of  water  and  to  discuss  the 
most  effective  methods  of  excluding  the  water  and  operating  the  properties. 

ACKNOWLEDGMENTS 

This  report  was  prepared  at  the  request  of  and  in  co-operation  with  the 
State  of  Arkansas,  whose  financial  aid  made  the  work  possible.  The  Univer- 
sity of  Arkansas,  the  Arkansas  Bureau  of  Mines,  Manufacture  and  Agricul- 
ture, and  the  State  Banking  Department  provided  funds. 

The  writers  wish  to  acknowledge  the  assistance  of  the  respective  de- 
partment chiefs,  Dr.  J.  C.  Futrall,  Jim  G.  Ferugson  and  W.  T.  Maxwell. 
Assistance  was  also  given  by  Messrs.  J.  A.  Brake,  State  Oil  and  Gas  In- 
spector; E.  E.  Winger,  Oil  and  Gas  Inspector  and  formerly  expert  driller 
for  the  Bureau  of  Mines,  and  John  J.  Doyle  of  the  Margay  Oil  Company. 

The  operators  and  others  familiar  with  local  conditions  kindly  furnished 
logs  of  wells,  production  records  and  miscellaneous  information.  Messrs. 


*BelI,  H.  W '.,  Petroleum  Engineer,  U.  S.  Bureau  of  Mines. 

•fKerr,  J.  B.,  Assistant  Petroleum  Technologist,  U.  S.  Bureau  of  Mines. 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


L.  W.  Mosburg  and  H.  W.  Hoots  of  the  U.  S.  Geological  Survey  co-operated 
in  the  collection  of  data.  •  The  El  Dorado  Chamber  of  Commerce  furnished 
space  and  equipment  for  field  headquarters. 

Thanks  are  extended  to  the  following,  who  co-operated  in  the  prepara- 
tion of  the  report:  Eugene  Holman,  P.  H.  Walber,  D.  B.  Harris  and  J.  L. 
Finley  of  the  Humble  Oil  &  Refining  Company;  J.  E.  Todd,  V.  C.  Megarity, 
W.  C.  O'Ferrell,  S.  C.  Strathers,  F.  Ray  McGrew,  F.  B.  Bimmel,  and  Howard 
Murphy,  of  the  Standard  Oil  Company  of  Louisiana;  E.  J.  Raisch  of  the 
Federal  Petroleum  Company;  H.  Gandy  and  J.  W.  Westmoreland,  of  Gulf 
Refining  Company;  J.  H.  Mann  and  C.  M.  Palmer,  of  the  Mann  Oil  Com- 
pany and  Imperial  Oil  Company;  J.  F.  Wright,  oil  lease  superintendent  and 
deputy  conservation  agent;  Roy  Wilson,  H.  S.  McGeath,  E.  D.  Holcomb,  of 
the  Magnolia  Petroleum  Company;  A.  J.  Jones,  Kansas  Gulf  Company;  E.  E. 
Windsor  Southwestern  Oil  Company;  Bradford  Hearn,  Shreveport  Pro- 
ducing and  Refining  Company;  Elton  Rhine  and  J.  T.  Lord,  of  the  Amerada 
Petroleum  Company;  J.  B.  Sowell  and  W.  M.  Coats,  of  the  El  Dorado  Natu- 
ral Gas  Company;  George  M.  Sonfield  and  Jos.  Parks,  Sun  Company;  J.  O. 
Nelson,  J.  P.  Smoots,  Arkansas  Natural  Gas  Company;  Elaine  Johnston, 
White  Oil  Corporation;  George  McPherson,  operator;  H.  W.  Holland,  El  Do- 
rado Petroleum  Company;  Charles  Carter,  drilling  contractor;  Ed  Hollyfield 
of  Hollyfield  et  al.;  C.  H.  Kampeter  of  Parry  Oil  Company;  D.  J.  &  J.  H. 
Johnson  of  Johnson  Drilling  Company;  H.  C.  Eddy  of  Petroleum  Rectifying 
Company;  A.  J.  Graff,  of  Constantin  Refining  Company;  H.  N.  Spofford, 
of  Gladys  Belle  Oil  Company;  A.  K.  Gordon  of  Louisiana  Oil  &  Refining 
Company;  G.  M.  LeGrande  of  the  Michigan-Arkansas  Oil  Company;  C.  E. 
Larder,  of  Sinclair  Oil  Syndicate. 

The  work  was  carried  on  under  the  general  direction  of  Mr.  A.  W. 
Ambrose,  Chief  Petroleum  Technologist  of  the  Bureau  of  Mines.  T.  E. 
Swigart  offered  many  helpful  suggestions  in  the  preparation  of  the  manu- 
script, and  W.  W.  Cutler  assisted  in  the  construction  and  preparation  of 
the  production  declines  and  appraisal  curves  and  data. 

The  writers  wish  to  express  appreciation  for  help  and  criticism  to  the 
following  members  of  the  Bureau  of  Mines;  R.  Van  A.  Mills,  W.  W.  Scott, 
W.  H.  Strang,  H.  H.  Hill,  J.  H.  Wiggins  and  W.  B.  Lerch. 


History  of  Development 

First  Wells: 

The  first  successful  well  in  the  El  Dorado  field  was  a  gas  well  brought 
in  by  the  Constantin  Oil  &  Refining  Company,  in  Section  12-18-16  (see  Map, 
Plate  A),  in  April,  1920.  This  gasser  had  an  initial  open  flow  capacity  of 
about  30,000,000  cubic  feet  per  day  and  a  rock  pressure  of  960  pounds  per 
square  inch.  Several  other  gas  wells  were  drilled  in  Section  12  and  in  the 
adjoining  Section  1.  Oil  did  not  begin  to  appear  in  these  wells  in  important 
quantities  for  some  months  and  only  shortly  before  the  oil  boom  was 
initiated  by  the  advent  of  the  Busey  well  did  they  show  oil  at  all.  These 
first  gas  wells  did  not  attract  much  attention  from  the  public,  probably 
because  the  Fort  Smith  gas  field  had  produced  no  oil  in  fifteen  years,  and 
it  was  the  general  impression  that  there  was  little  likelihood  of-  finding  oil 
at  El  Dorado. 

During  the  latter  part  of  August,  1920.  drilling  operations  were  started 
on  the  Armstrong  farm  in  the  NW*4  of  Section  31-17-15  by  Mitchell  and 
Bonham.  Considerable  mechanical  difficulty  and  financial  trouble  were 
encountered  in  drilling  this  well  and  it  has  been  reported  that  the  hole  was 
twice  abandoned  and  the  derrick  skidded  a  short  distance  for  a  fresh  start. 
Dr.  S.  T.  Busey  became  interested  in  the  well  and  assisted  in  pushing  the 
work  to  a  successful  conclusion.  The  well  came  in  January  10,  1921,  with 
a  large  amount  of  gas  and  an  oil  production  probably  exceeding  5,000  bar- 
rels per  day.  This  well  has  since  been  known  as  the  Busey  well. 

The  Busey  well  was  drilled  with  rotary  tools  and  that  practice  has 
been  followed  for  all  other  wells  in  the  field.  In  a  few  instances,  wells  have 
been  finished  with  cable  tools.  Adequate  precautions  were  not  taken  and 
the  Busey  well  blew  wild  for  some  time.  The  ground  and  foliage  were 
sprayed  with  oil  for  a  considerable  area  about  the  derrick.  After  about 
fifteen  days  blowing  wild,  water  began  to  appear  and  the  fluid  turned  to  a 
brownish  color.  Efforts  to  control  the  well  were  unsuccessful.  The  water 
increased  rapidly  until  the  oil  and  gas  were  completely  choked  off,  limiting 
the  well's  productive  life  to  about  forty-five  days. 


EL  DORADO,  ARK..  OIL  AND  CAS   FIELD  9 

In  drilling  the  Busey  well,  sand  and  lignite  were  logged  at  1171-1180  feet 
and  1201-1211  feet.  The  log  is  not  complete,  but  shows  the  lower  formations 
as  follows: 

2052-2062  feet— shale. 
2062-2072  feet— lime,  rock,  gas. 
2072-2073  feet — gumbo. 
2073-2176  feet— not  logged. 
2176  feet — top  of  sand. 
2223  feet — total  depth. 

The  well  had  either  been  drilled  too  deep  or  "drilled  itself"  into  bottom 
water  by  the  unrestrained  flow  of  gas.  It  is  likely  also  that  the  top  water 
had  not  been  excluded.  After  the  oil  production  had  been  completely 
drowned  out,  plans  were  made  to  repair  the  well,  in  order  to  protect  the 
surrounding  territory  and  to  make  the  well  produce  again.  On  account  of 
the  double  source  of  water  and  the  large  quantity  of  formation  that  had 
been  removed  during  the  blj»ving  period,  E.  E.  Winger,  then  with  the  Con- 
servation Commission  of  Arkansas,  advised  that  the  well  be  abandoned. 


Plate  I — Busey  Well  (shown  in  foreground)  Section  31-17-15,  the  first 
oil  well  completed  in  the  El  Dorado  Field.  Well  began  producing  January 
10,  1921.  Photo  taken  after  abandonment  of  well. 

"  • 2-1 

The  well  was  abandoned  during  the  latter  part  of  April,  1921.  under 
the  direction  of  Mr.  Winger  and  Mr.  J.  A.  Brake,  State  Oil  and  Gas  In- 
spector. The  abandonment  work  included  cleaning  out  to  bottom,  with  the 
hole  full  of  water,  placing  90  sacks  of  thickly-mixed  cement  on  bottom  with 
a  dump  bailer,  and  filling  the  hole  full  of  mud  to  the  surface.  The  recom- 
mendation to  apply  extra  pump  pressure  to  the  cement  in  the  hole  was  not 
carried  out,  principally  on  account  of  the  scarcity  of  suitable  equipment  at. 
that  time.  Plate  1  shows  the  Busey  well  and  surrounding  wells  (Septem- 
ber, 1921).  The  scarcity  of  derricks  in  its  immediate  vicinity  is  noticeable. 

Before  the  end  of  March,  1921,  about  twenty  oil  producers  had  been 
completed.  The  majority  of  these  wells  were  drilled  in  a  southerly  direction 
from  the  Busey  well.  The  second  and  third  oil  producers  were  located  in 
Section  6-18-15,  the  next  six  in  Section  31-17-15;  then  one  in  Section  5-18-15. 
one  in  Section  32-17-15,  one  in  Section  25-17-16,  two  in  Section  7-18-15,  one 
in  Section  30-17-15,  four  in  Section  31-17-15,  and  one  in  Section  5-18-15.  The 
development  spread  rapidly  to  the  south  as  the  productive  area  was  found 
to  extend  only  about  a  mile  to  the  north  of  the  discovery  well. 

Table  1  shows  the  number  of  producing  wells,  oil  production  and  deliv- 
eries, stocks,  and  other  data  by  months  from  January  to  October,  1921.  The 
Total  oil  production  of  10,380,000  barrels  is  estimated  and  meant  to  include 
evaporation  losses,  seepage  and  other  lease  losses,  fuel  burned  in  field,  oil 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


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EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 11 

used  in  local  refineries,  tank  car  deliveries,  pipe-line  deliveries  and  storage 
oil  at  the  end  of  October.     Some  of  the  factors  are  admittedly  difficult  of 
estimation,  but  it  is  reasonably  certain  that  at  least  10,000,000  barrels  of  oil 
had  been  removed  from  the  underground  reservoir  by  November  1,  1921. 
Acreage  and  Oil   Prices: 

Following  the  completion  of  the  Busey  well,  which  initiated  the  boom, 
the  area  within  a  radius  of  several  miles  from  the  discovery  well,  was 
leased  by  individuals  and  corporations.  The  prices  paid  for  leases  ranged 
from  a  few  dollars  to  $5,000  per  acre,  depending  primarily  on  the  distance 
and  amount  of  the  nearest  production. 

The  only  outlet  for  the  first  production  was  by  tank  cars.  It  was  for- 
tunate that  the  discovery  well  was  so  close  (about  two  miles)  to  El  Dorado, 
a  town  of  about  5,000  population  and  served  by  two  railroads.  Most  of  the 
first  oil  marketed  brought  as  low  as  30  cents  per  barrel.  Some  of  it  is 
reported  to  have  been  sold  at  that  figure,  even  after  The  Louisiana  Oil  & 
Refining  Company  opened  its  6-inch  pipe  line  on  June  24,  1921.  This  com- 
pany paid  40  cents  per  barrel  for  oil  below  34  degrees  Baume  gravity,  and 
50  cents  per  barrel  for  oil  above  that  gravity.  On  June  17,  the  Standard  Oil 
Company  posted  a  schedule  of  50  cents  per  barrel  for  oil  less  than  33° 
gravity,  60  cents  for  33°  to  35'  gravity  and  70  cents  per  barrel  for  oil  above 
35°  gravity.  On  September  22  the  price  went  to  80  cents  and  90  cents  for 
oils  below  and  above  34°  Baume  gravity.  The  maximum  limit  for  water 
and  sediment  was  3  per  cent.  Some  of  the  small  purchasers  were  paying 
a  premium  of  about  10  cents  per  barrel. 

Prior  to  August  15,  1921,  considerable  oil  was  sold  at  figures  below  the 
posted  prices  of  the  larger  purchasers  on  account  of  the  storage  conges- 
tion. It  is  reported  that  a  scale  of  30,  40  and  45  cents  per  barrel  was  in 
effect  simultaneously  with  the  higher  schedules  and  that  the  smaller  pur- 
chasers often  selected  only  the  oil  that  exceeded  34  gravity  and  that  ran 
less  than  2.5  per  cent  B.  S.  and  mud.  These  circumstances  appear  to  have 
worked  some  discrimination  against  the  small  purchaser  after  the  conges- 
tion was  relieved.  By  the  end  of  October,  1921,  the  top  price  per  barrel 
had  reached  $1.50,  and  at  present  (January.  1922)  the  posted  price  is  $1.75 
lor  all  oil  under  34"  Baume,  and  $2.00  per  barrel  for  34  Baume  and  above. 

Storage  and    Marketing   Facilities: 

At  the  end  of  October,  1921,  nearly  4,000,000  barrels  of  storage  had  been 
erected.  It  was  composed  of: 

61 — 55,000  barrel  steel  tanks 3,355,0:)0  barrels 

9 — 37,500  barrel  steel  tanks 337,500  barrels 

Miscellaneous  250,000  barrels 

3,942,500  barrels 

The  Louisiana  Oil  &  Refining  Company  began  pumping  through  its  6- 
inch  line  June  24,  1921.  The  Standard  Oil  Company  of  Louisiana  started  to 
operate  its  8-inch  Hue  on  June  26,  1921,  and  the  Shreveport-El  Dorado  Pipe 
Line  Company  first  moved  oil  through  its  8-inch  on  August  9,  1921. 

Seventeen  loading  racks  with  a  total  capacity  of  401  tank  cars,  or  about 
80,000  barrels,  of  oil  daily  were  in  operation  for  tank  car  transportation  by 
the  middle  of  July,  1921. 

There  are  twelve  local  refining  plants  of  varying  capacities  and  pur- 
pose. They  have  handled  only  a  small  proportion  of  the  output  of  the  field 
up  to  November,  1921.  The  following  list  covers  those  operating  in  Jan- 
uary, 1922: 

Capacity 
Name  Bbls.  per  Day 

Airdale  Oil  &  Refining  Company 500 

Arkansas  P.  &  R.  Company 2/JOO 

Abner   Davis   Ret.   Company 500 

El  Dorado  Oil  Ref.  Company 2,000 

Orison   Ref.   Company 5,000 

Jones,  R.  C 800 

Lion  O.  &  R.  Company 5,000 

New-Ark  Pet.  Corporation 2,500 

Petroleum   Products  Company 2,000 

Red  River  Refining  Company 1,500 

Shippers    Petroleum    Company 2,090 

Union  Pipe  Line  &  Refining  Company 3,000 

26,800 


12  EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

State  Conservation   Commission: 

The  original  Arkansas  law  dealing  with  the  conservation  of  oil  and  gas 
was  passed  toy  the  Legislature  in  1917.  On  February  18.  1921,  thirty-nine 
days  after  the  first  commercial  production  of  oil  in  the  State,  Act  No.  144 
was  approved.  This  Act  supplemented  the  basic  law  of  1917  and  furnished 
a  workable  law  for  the  Conservation  Commission.  The  State  laws  relating 
to  oil  and  gas  are  published  in  a  State  Report  entitled  "Minerals  in  Arkan- 
sas." 

The  Conservation  Commission,  headed  by  J.  A.  Brake,  has  been  handi- 
capped financially  and  has,  therefore,  been  unable  to  extend  supervision  to 
all  of  the  important  features  connected  with  development.  However,  it  did 
good  work  insofar  as  its  funds  and  personnel  permitted. 

The  prnicipal  regulations  which  the  Commission  attempted  to  enforce 
are,  in  substance,  as  follows: 

(1)  Wells  that  produce  gas  must  be  closed  in  and  used  for  fuel 
purposes   solely.     The   tendency   was   to   waste   enormous 
quantities  of  gas  in  an  effort  to  "blow  a  well  in"  to  oil  pro- 
duction. 

(2)  The    casinghead    control    fittings,    usually    known    as    a 
"Christmas    Tree"    (see    Plate    XV)    equipment    must    be 
heavy  enough  to  insure  safety  under  the  pressure  obtain- 
ing and  be  constructed  in  a  manner  to  insure  control  of  the 
well  in  case  of  emergency. 

(3)  Each  well  shall  be  cased  with  at  least  two  strings  of  pipe, 
the  first  landed  and  cemented  with  at  least  25  sacks  of 
cement  at  about  200  feet,  and  the  second  landed  and  ce- 
mented with  at  least  60  sacks  of  cement  at  a  short  distance 
above  the  oil  sand. 

(4)  Abandonment  of  wells  shall  be  accomplished  with  the  use 
of  mud  or  cement  or  both  in  a  manner  adaptable  to  the 
particular  case  and  satisfactory  to  the  Commission. 

At  present,  there  is  no  money  appropriated  or  tax  levied  to  carry  on  the 
conservation  work  in  the  State.  Because  of  the  treacherous  nature  of  op- 
erating conditions,  supervision  by  a  commission  of  competent  engineers 
should  result  in  large  savings  of  oil  and  gas.  It  would,  therefore,  be  desir- 
able to  provide  an  adequate  annual  budget  for  such  a  commission,  in  order 
to  insure  a  definite  and  complete  program  of  conservation.  This  work  is  of 
great  importance  at  this  time,  because  of  the  opportunities  to  effect  con- 
servation in  a  new  field.  Once  a  field  has  been  improperly  drilled,  it  is 
usually  difficult  and  expensive  to  repair  the  damage.  If  a  new  field  is  dis- 
covered in  Arkansas  a  trained  personnel  would  be  equipped  to  meet  the  sit- 
uation. 

Co-operation   by  the   U.  S.   Bureau   of   Mines: 

By  the  middle  of  March,  1921,  the  situation  at  El  Dorado  had  become  a 
serious  problem  from  the  standpoint  of  conservation.  Assistance  from  the 
Bureau  of  Mines  was  requested  by  the  Conservation  Commission,  upon  the 
advice  of  J.  H.  Mann  of  the  Imperial  Oil  &  Gas  Company.  Accordingly. 
E.  E.  Winger,  consulting  driller  of  the  Dallas,  Texas,  office,  was  detailed 
to  the  work.  J.  B.  Kerr,  petroleum  engineer,  was  later  sent  from  Dallas  to 
render  further  assistance. 

The  bureau  men  conferred  with  operators  and  did  work  on  wells  for 
the  exclusion  of  water  by  means  of  cement,  which  had  to  be  properly  mixed 
and  placed.  At  times,  this  involved  the  use  of  extra  closed-in  pressure.  In 
some  cases,  cement  was  placed  behind  the  casing  to  shut  off  top  water,  and 
again  bottom  water  had  to  be  shut  off  by  cement. 

About  the  middle  of  April,  1921,  Mr.  Winger  resigned  from  the  Bureau 
of  Mines  and  joined  the  forces  of  the  Conservation  Commission  of  Arkansas. 
He  made  notable  progress  in  introducing  efficient  methods  of  finishing  wells 
and  excluding  water.  J.  B.  Kerr  made  drawings  illustrating  methods  and 
appliances  and  constructed  a  contour  map,  showing  the  shape  of  the  top 
of  the  productive  oil  sand. 

In  August,  1921,  the  Bureau  was  able  to  assign  the  senior  author  to 
the  El  Dorado  field  and,  with  the  assistance  of  J.  B.  Kerr.  sufficient  field 
work  was  done  to  warrant  the  compilation  of  this  report. 


EL  DORADO,  ARK.,  OIL  AND  (JAS  FIELD  13 


Drilling  Methods 


Equipment  and   Power: 

The  use  of  rotary  drilling  is  rapidly  increasing,  especially  in  loose  for- 
mations, and  it  is  now  used  in  practically  all  loose  or  soft  formations  that 
are  deep  enough  to  justify  the  expense  of  its  installation.  Factors  working 
against  rotary  installation  are: 

(1)  Usually,  a  very  poor  well  log  is  obtained,  and  many  forma- 
tions capable  of  production  have  been  passed  by  without 
testing.     In  general,  the  contents  of  sands  are  not  so  well 
known  in  rotary  drilled  fields  as  in  a   cable  tool  drilled 
field,,   and   this   results   in  more   wells   being   drilled   into 
water; 

(2)  When   the   formations    are   very   porous,    considerable    ex- 
pense is  necessary  for  extra  mud  to  mud  off  the  porous- 
mud-absorbing  formation  and  thus  allow  continuous  circu- 
lation ; 

(3)  When  the  formations  are  hard  and  stand  up  well  without 
mudding,  cable  tools  can  be  used  to  advantage,  as  long 
strings  of  casing  can  be  inserted  in  the  open  hole; 

(4)  When  there  are  frequent  changes  in  formation,  from  such 
as  hard  rock  to  clay  or  gumbo,  a  continual  change  from 
rock  bits  to  fish-tail  bits  is  necessary  because  of  the  "gum- 
ming up"  of  the  cone  bits  in  soft,  sticky  material,  and  this 
causes  delay. 

The  success  of  cable  tools  in  the  El  Dorado  field  is  not  known,  but  it 
is  probable  that  on  account  of  the  loosely  consolidated  formations,  it  would 
be  more  difficult  and  costly  than  the  rotary  method.  The  wells  of  the  El 
Dorado  field  have  been  drilled  to  the  last  water  shut-off  point,  in  every  case, 
with  rotary  tools.  The  rotary  equipment  used  has  varied  in  character  from 
old  style  to  new  style  rotaries.  Four-inch  drill  pipe  has  been  used  through- 
out the  greater  portion  of  the  hole.  So  far,  no  installations  of  high-power 
twin  cylinder  steam  engine  rotaries  have  been  reported.  A  few  wells  have 
been  drilled  with  gas  engines  and  satisfactory  results  are  reported.  The 
comparatively  easy  drilling  at  El  Dorado  makes  feasible  the  use  of  gas 
engines  of  ordinary  sizes.  The  boiler  installation  can  thereby  be  greatly 
reduced  and  of  sufficient  size  to  meet  the  needs  of  operating  the  pumps  and 
forge.  The  gas  engines  are  equipped  with  an  electric  magneto,  an  electric 
Wyco  coil  type  or  compressioi»hot  point  system  of  ignition.  The  old  system 
of  hot  tube  ignition  is  not  used  in  this  work,  because  of  its  unreliability 
and  the  danger  of  an  open  flame  in  a  gas-producing  area.  It  is  necessary 
to  use  an  ignition  system  that  can  be  correctly  adjusted  by  the  men 
available,  because  of  the  excessive  strains  in  the  engine  and  loss  of  power 
which  results  from  improper  timing. 

Electric  power  for  drilling  has  not  been  used  at  El  Dorado,  Arkansas. 
Although  electric  drilling  has  proven  efficient  and  economical  in  other  fields, 
its  introduction  in  Southern  Arkansas  has  been  retarded  by  the  absence  of 
available  power  (unless  private  generating  plants  are  constructed)  and  by 
the  lack  of  familiarity  of  the  local  operators  with  the  system.  It  is  true 
That  more  energy  can  be  developed  with  oil  or  gas  by  means  of  internal 
combustion  engines  than  by  generating  steam  with  the  same  fuel.  How- 
ever, economy  of  power  does  not  always  dictate  the  practice  in  oil  and  gas 
fields,  where  gas  is  cheap  and  not  marketable. 

The  generation  of  electricity  by  means  of  internal  combustion  engines 
has  proven  economical  in  many  cases  for  drilling  and  general  use  on  oil 
properties.  This  is  especially  true  when  cheap  gas  is  not  available  and  oil 
is  used  as  the  explosive  fuel.  Under  certain  conditions,  it  is  more  econom- 
ical to  generate  electricity  with  steam  turbines  and  transport  it  by  power 
lines  than  to  use  the  steam  direct  through  long  uninsulated  pipe  lines. 
There  are  many  factors  that  determine  the  most  practicable  power  to  use 
for  drilling.  Mechanically,  steam  is  well  adapted  to  the  work  and  because 
of  the  abundance  of  gas,  with  a  limited  market,  it  was  used  extensively  in 
the  El  Dorado  field. 

In  the  fields  where  it  has  been  tried,  the  electric  motor  for  dri'ling  has 
proven  satisfactory  from  a  mechanical  standpoint  for  both  standard  and 
rotary  work  and  very  often  reduces  the  cost  of  operations.  A  75-horse- 


14 EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

power  motor  is  usually  installed  for  drilling  and  a  40-horse-power  motor  To. 
the  mud-circulating  pumps.  The  principal  advantages  over  steam  operation 
are  the  omission  of  boiler  installations  and  repairs  and  almost  complete 
elimination  of  water  requirements. 

Casing   Programs: 

Wells  in  this  field  are  cased  with  at  least  two  strings  of  pipe,  the  first 
being  l2l/2-inch  or  10-inch  conductor  pipe  which  is  cemented  at  about  200 
feet  and  the  other  a  water  string  of  usually  ti-inch  8-thread  pipe.  In  some- 
wells,  8-inch  pipe  has  been  used  as  a  second  string,  but  probably  in  no  case 
has  it  been  used  as  the  final  water  string.  The  general  practice  has  been 
to  check  the  hole  and  casing  measurement  with  a  steel  tape.  Some  serious 
errors  in  measurements,  however,  are  reported  to  have  resulted  in  casing 
off  oil  or  drilling  into  water.  It  is  practically  impossible  to  know  the  exact 
depth  of  the  hole  by  adding  the  figures  for  lengths  of  joints  of  casing. 

The  smaller  pipe  used  in  El  Dorado  usually  has  8  threads  per  inch. 
The  larger  sizes  having  10  threads  per  inch  are  12%-inch  40  pounds;  10- 
inch  32  and  35  pounds;  S^t-inch  32  pounds.  Sizes  of  casing  having  8  threads 
per  inch  are  8-inch  29.2  pounds  and  6-inch  19.5  pounds.  The  liners  are  dif- 
ferent weights  of  4-inch  to  41/£-inch  pipe. 

There  have  been  no  cases  of  collapsed  casing  reported  to  the  writers 
thus  far,  because  El  Dorado  operators  in  most  cases  used  good  weights  of 
casing  for  the  depths.  Comparatively  shallow  depths  to  the  shut-off  point 
and  small  sizes  of  casing  used  have  also  assisted  in  preventing  collapse. 
In  Table  No.  2  (a),  the  collapsing  depths  of  various  casings  are  shown  in 
connection  with  the  other  data.  Table  No.  3  (b)  shows  the  amounts  of 
cement  required  for  different  sizes  of  casings  and  holes.  Both  of  these 
tables  were  prepared  at  the  Denver,  Colorado,  office  of  the  U.  S.  Bureau  of 
Mines,  under  the  direction  of  F.  B.  Tough. 

In  selecting  casing  for  a  water  string,  attention  should  be  given  to  its 
weight  in  order  to  avoid  collapse  by  outside  water  or  mud  pressure.  How 
ever,  collapsed  casing  cannot  be  prevented  when  formations  shift.  The  best 
practice  is  to  choose  a  string  of  casing  that  will  stand  the  fluid  pressure  at 
the  prescribed  depth  with  a  safety  factor  of  two.  If  a  given  size  and  weight 
of  casing  is  supposed  to  collapse  by  an  external  pressure  due  to  3,000  feet 
of  effective  water  column  (1,302  pounds  per  square  inch),  that  casing  should 
not  be  used  to  a  depth  greater  than  about  1,500  feet  below  the  natural  water 
level  outside  the  casing  unless  enough  cement  is  used  to  protect  a  con- 
siderable length  of  the  lower  portion  of  the  casing.  When  rotary  drilling  is 
employed,  the  gravity  of  the  mud  and  the  full  column  outside  the  pipe  to 
the  surface,  must  be  considered.  For  example,  if  the  rotary  mud  back  of 
the  casing  has  an  average  specific  gravity  of  1.25  (25  per  cent  heavier  than 
water)  or  5/4  the  weight  of  water,  a  given  string  of  casing  for  safety 
should  have  an  effective  column  of  mud,  on  the  outside  of  the  pipe,  of  only 
4/5  of  the  safe  depth  for  clear  water  as  recorded  in  Table  II.  Another  way 
to  arrive  at  the  safe  depth  for  casing  in  mud  is  to  divide  the  safe  water 
depth  by  1.25.  or  whatever  happens  to  be  the  specific  gravity  of  the  mud. 
If  it  could  be  assumed  that  the  fluid  standing  outside  of  the  casing  would 
remain  undisturbed,  a  factor  of  safety  1.5  or  1.4  might  be  considered.  Earth 
tremors  and  shifting  of  formation  may  have  considerable  water-hammer 
effect,  regardless  of  whether  the  walls  actually  squeeze  the  casing. 

It  is  usually  found  economical  for  deep  wells,  to  make  up  suitable  com- 
bination strings  with  the  heaviest  pipe  on  the  bottom  and  the  lengths  oi 
the  lighter  weights  proportioned  according  to  their  safe  depths.  In  many 
oil  fields,  two  different  weights  of  pipe  are  often  used,  but  a  combination  of 
three  is  less  common.  As  far  as  is  known  by  the  writers,  no  combination 
strings  have  been  used  at  El  Dorado. 
Testing  Formations: 

In  at  least  the  first  work  of  developing  underground  deposit ;  of  oil  and 
gas  in  any  area,  drilling  methods  should  be  modified  in  such  manner  as  to 
give  the  most  accurate  knowledge  of  formations  and  their  fluid  content. 
There  are  many  examples  of  wildcat  wells  condemning  territory  by  passing 
through  commercial  deposits  without  testing  them  and,  in  some  case?, 
without  suspecting  their  presence.  There  are  also  many  instances  where 
high-pressure  oil  and  gas  have  been  found  without  any  particular  care  being 
taken,  but  where  the  preseiice  or  capacity  of  upper  deposits  remain  un- 
known, and  the  exact  nature  of  -the  producing  horizon  was  not  learned.  Oil 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


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16  EL   DORADO.  ARK.,  OIL  AND  OAS  FIELD 


deposits  that  are  now  commercially  productive  or  that  may  become  so 
within  a  reasonable  period,  should  be  protected  from  infiltrating  water  and 
from  dissipation  into  other  strata.  Without  a  comprehensive  knowledge  of 
all  of  the  formations  penetrated,  it  is  impossible  to  know  whether  and  how 
to  protect  strata  for  future  use. 

In  some  fields,  cable  tool  drilling  is  generally  the  best  adapted  to  the 
accurate  determination  of  underground  conditions.  Unfortunately,  this 
method  cannot  be  used  in  many  fields,  because  of  the  soft  and  caving  nature 
of  the  formations.  Satisfactory  results  can  be  obtained  with  the  rotary  sys- 
tem if  sufficient  care  is  exercised.  In  order  to  obtain  adequate  knowledge 
with  rotary,  samples  should  be  taken  from  the  ditch  at  least  every  ten  feet 
of  hole  made.  The  speed  of  the  upward  current  of  mud  should  be  figured  and 
the  samples  checked  back,  through  the  time  interval,  against  the  feel  of 
the  tools  and  action  of  the  pumps.  As  the  driller  relies  mainly  on  the  feel, 
to  detect  a  change  of  formations,  cuttings  should  be  studied  with  relation 
to  changes  noted  iby  the  feel.  Samples  of  porous  material  should  be  care- 
fully examined  to  determine  the  fluid  content.  When  practicable,  the  core 
barrel  should  be  used  repeatedly  when  nearing  the  productive  horizons. 
The  core  is  a  correct  sample  of  the  formation  and  will  usually  disclose  the 
presence  of  any  oil  in  the  stratum.  The  future  of  accurate  information 
obtained  from  rotary-drilled  wells  is  dependent  to  a  large  extent  on  a  prac- 
ticable method  of  sampling  formations  and,  at  present,  the  core  barrel 
seems  to  have  the  most  promise. 

It  is  advisable  to  test  a  sample  from  the  ditch  with  chloroform,  ether 
or  carbon  tetrachloride,  in  order  to  indicate  the  presence  or  absence  of  oil. 
In  making  this  test,  the  sample  should  be  thoroughly  shaken  with  the  sol- 
vent and  allowed  to  settle  for  some  time  and  the  liquid  then  run  through 
white  filter  paper.  If  petroleum  is  present  in  appreciable  quantities,  a  dark 
ring  will  appear  on  the  filter  paper. 

In  general,  ditch  samples  are  obtained  in  two  ways.  Some  drillers  thin 
The  mud,  while  others  thicken  it  and  increase  the  speed  of  circulation.  Both 
methods  possess  merit  and  are  usable  for  the  same  general  purpose,  though 
the  principles  are  somewhat  different.  Thinning  the  mud  lightens  the 
weight  of  the  column  of  liquid  in  the  hole  and  decreases  the  pressure  oppo- 
site the  sand,  so  that  any  oil  or  gas  can  come  into  the  hole  more  easily. 

Gas  is  somewhat  soluble  in  water.  Methane,  the  largest  constituent  of 
natural  gas,  is  3.9  per  cent  (*)  soluble  in  water  at  ordinary  temperature 
and  pressure.  It  is  probably  much  more  soluble  at  the  increased  pressures 
obtaining  underground  on  account  of  the  compressibility  of  gas  and  the  non- 
compressibility  of  water.  The  solubility  of  gas  in  water  assists  it  in  trav 
eling  from  the  formation  to  the  hole,  because  when  a  substance  is  dissolved 
in  a  liquid,  it  tends  to  diffuse  equally  to  all  parts  of  the  liquid.  Hence,  solu- 
bility and  diffusion  help  to  explain  why  a  gas  is  able  "to  show"  when  the 
fluid  pressure  exceeds  the  rock  pressure.  Such  a  condition  may  exist  when 
the  sand  is  not  taking  water  and  a  condition  of  stability  exists.  When  the 
gas  enters  the  hole,  it  rises  through  the  water  on  account  of  the  difference 
in  weight  and  the  high  fluidity  of  the  water.  Thin  mud  then  gives  the  gas 
and  oil  a  better  opportunity  to  enter  the  hole.  There  are,  however,  many- 
deposits  that  will  not  "show"  against  a  hole  lull  of  muddy  water  or  even 
clear  water.  If  light  gravity  oil  shows  under  such  conditions,  it  is  manifest 
that  there  is  considerable  pressure  to  force  it  into  the  hole. 

When  mud  is  thickened  and  the  speed  of  circulation  increased,  larger 
particles  of  formation  are  buoyed  up  and  discharged  at  the  surface.  In 
this  way,  particles  as  large  as  peas  may  be  obtained  in  the  samples.  If  the 
thick  mud  does  not  wash  through  such  pieces,  they  will,  in  some  cases, 
indicate  the  presence  or  absence  of  oil  by  solvent  test  or  bv  more  inser- 
tion. This  method  oftentimes  gives  an  indication  of  the  presence  of  gas  as 
well,  for  the  gas  will  "show  on  the  ditch"  in  the  form  of  babbles  which  rise 
to  the  surface  of  the  mud  and  burst. 

When  the  rock-pressure  is  not  sufficient  to  expel  the  mud  and  water 
from  the  hole,  the  only  means  of  estimating  the  productivity  of  the  sand  is 
to  lower  or  remove  the  drilling  fluid  from  the  hole  by  bailing.  Even  that 
is  sometimes  not  sufficient  to  prove  commercial  production,  and  swabbins 

*  Hill,  H.  H.  Supt.,  i'.  S.  Bureau  of  Mines  Experiment  Station.  Bartlcsrillc. 
Oklahoma — personal  rotniiniitication. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


17 


or  rewashing  is  resorted  to  in  order  to  bring  in  the  oil  or  gas.  It  is,  of 
course,  necessary  to  fully  protect  the  walls  of  the  hole  from  caving  while 
making  a  bailing  test.  The  usual  procedure  in  such  a  test  is  to  remove  the 
drill  stem  and  insert  the  pipe  with  a  packer  and  with  a  suitable  amount  of 
perforation  so  placed  as  to  be  opposite  the  formation  to  be  tested  when  the 
pipe  is  set. 

If  complete  data  of  other  wells  are  collected  and  compiled  by  the  en- 
gineer for  the  purpose  of  selecting  depths  to  test,  it  becomes  relatively  easy 
to  test  at  those  depths.  For  instance,  if  it  is  desired  to  make  a  test  of  the 
formation  between  1,160  and  1,200  feet,  the  drill  hole  can  be  stopped  at 
about  1,150  feet  in  a  tapered  hole  and  the  casing  set  without  perforations. 
A  small  hole  can  then  be  drilled  ahead  to  the  desired  depth  and  the  mud 
bailed  from  the  casing  without  much  danger  of  disturbing  the  mud  and 
formations  on  the  outside  of  the  casing.  When  the  oil-bearing  formation 
has  already  been  passed  through,  which  is  often  the  case,  the  pipe  is  usually 
set  on  bottom  and  some  sort  of  suitable  packer  attached  above  the  per- 
forated portion  in  order  to  retain  the  mud.  The  so-called  mother-hubbard 
packer  of  the  inverted  umbrella  type  and  made  of  canvas,  burlap,  rope  or 
leather,  has  been  used  with  success  and  economy  for  such  work.  In  many 
cases,  such  a  packer  does  not  effectively  exclude  top  water,  and  in  that 
event  the  test  is  of  little  or  no  value.  Enough  packing  material  should  be 
used  to  insure  against  buckling  past  and  down  the  casing.  The  telescoping 
packers,  carying  rubber  or  hemp,  also  are  used.  For  their  successful  use, 
the  bore-hole  should  be  circular  and  smooth  and  of  about  the  diameter  ex- 
pected. A  hard  shell  to  set  this  type  of  packer  in  is  also  desirable. 

If  a  temporaray  shut-off  can  be  effected,  the  mud  should  be  slowly  bailed 
from  the  casing,  after  providing  the  proper  control  fittings.  Obviously, 
these  appliances  are  likely  to  be  of  little  use  for  high-pressure  unless  means 
are  provided  for  retaining  the  pressure  on  the  outside  of  the  casing.  It  is 
desirable  to  braden-head  the  casing  to  the  conductor  pipe  or  other  string  of 
casing,  else  there  will  be  danger  of  a  well  blowing  wild  outside  of  the 
casing. 

Plate  II  shows  a  crew  in  the  El  Dorado  field  bailing  down  the  mud  in 
a  well  that  is  expected  to  come  in  any  minute.  Gas  has  already  appeared 
in  this  well.  The  "Christmas  Tree'  is  fitted  with  a  valve  below  and  one 
above  the  lead  lines.  In  case  the  well  should  blow  in  with  high  gas  pres- 
sure, both  valves  can  be  closed  on  the  sand  line.  The  only  waste  would  be 
a  spray  around  the  line,  but  the  main  flow  of  oil  would  be  diverted  through 
the  lead  lines  shown  in  the  foreground. 


Plate    II — Bailing    Down   to   Bring   in   Well.     Connections    Made  for   Flowing 

Well. 


18  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

The  practice  at  El  Dorado  of  cementing  a  conductor  string  at  about 
200  feet,  is  an  excellent  one.  If  this  is  done,  any  formation  can  be  safetly 
tested  by  braden-heading  or  packing  off  between  the  testing  string  and  the 
conductor.  It  may  be  argued  that  the  upper  showings  at  El  Dorado  are 
known  to  be  of  low  pressure  and  of  little  commercial  importance,  because 
a  few  tests  have  indicated  that  condition.  The  main  oil  zone  in  the  field 
is  apparently  not  uniform  and  the  upper  strata  in  general  are  also  irregular 
in  occurrence.  It  is  quite  possible,  then,  that  upper  horizons  may  occur 
"which  are  commercially  productive  in  certain  areas  and  that  the  few  tests 
have  not  been  conclusive. 

The  mad  scramble  with  which  operators  conducted  their  rotary  drilling, 
jn  order  to  reach  the  known  productive  zone  has  resulted  in  meager  infor- 
mation concerning  the  nature  of  the  upper  deposits.  A  number  of  wells 
.have  logged  showings  of  oil  or  gas.  For  instance,  a  strong  showing  of  gas 
and  oil  in  twenty  feet  of  good  sand  was  reported  at  1,800  feet  depth  in  a 
well  on  Section  8-18-15.  This  deposit  was  mudded  off  in  the  usual  way.  If 
the  correct  gravity  of  the  upper  oil  could  be  obtained,  it  would  aid  in  an 
estimation  of  its  value.  It  is  obvious  that  if  a  bed  of  tar  or  very  heavy  oil 
is  penetrated,  it  will  probably  be  noted  on  the  ditch,  for  the  reason  that  it 
is  not  readily  driven  back  into  the  strata  by  the  mud  and  water  and  sticks 
together  better  than  lighter  oil.  When  light  oil  shows  in  the  presence  of 
•a  full  column  of  mud,  there  is  apt  to  be  considerable  pressure  behind  it  and 
it  is  worth  testing  to  determine  its  productivity. 

If  there  are  upper  oil  and  gas  deposits  of  present  or  near-future  com- 
mercial value,  that  fact  should  be  known  before  the  wells  are  finished,  and 
adequate  provision  made  to  protect  them.  Before  the  wells  in  a  certain 
district  are  abandoned,  enough  tests  should  be  made  to  determine  the  pos- 
sibility of  utilizing  the  upper  sands.  It  is  obvious  that  if  upper  production 
is  obtained,  it  must  be  protected  from  any  top  water  lying  below  about  200 
feet.  So  far,  no  special  attention  has  been  given  to  the  protection  of  any 
upper  oil  sands  from  top  water,  and  on  this  account  it  may  be  impossible 
later  to  get  a  fair  test  of  the  upper  sands  until  the  upper  water  is  excluded. 

In  this  connection  it  should  be  mentioned  that  the  mud-fluid  column 
cannot  always  be  relied  upon  to  protect  upper  oil  sands  against  water  in- 
filtration, especially  with  the  common  method  of  circulation  with  no  extra 
closed-in  pump  pressure.  In  older  fields,  gas  is  often  found  issuing  from 
behind  casings  landed  with  rotary.  As  time  elapses,  even  thick  rotary  mud 
may  gradually  settle  out  and  allow  gas  to  blow  out  and  water  to  travel  from 
its  native  formation.  The  results  of  such  action  are  illustrated  in  A  and  B 
of  Plate  III.  Thus  a  valuable  deposit  of  oil  may  be  somewhat  flooded  with 
water  before  production  is  attempted.  The  time  to  protect  oil  deposits 
from  water  and  from  dissipation  into  low-pressure  porous  strata  is  during 
the  drilling  of  the  wells. 

This  discussion  is  not  a  prediction  that  extensive  valuable  upper  de- 
posits exist.  The  possibility  exists  and  a  more  thorough  inventory  should 
be  made  by  conducting  tests  whenever  possible.  When  drilling  is  done  by 
contractors,  a  qualified  representative  of  the  company  should  keep  almost 
constant  watch  of  the  samples  and  should  be  able,  under  the  contract,  to 
make  a  complete  test  at  any  point  desired. 

Completing  Wells: 

In  order  to  avoid  serious  mistakes,  when  drilling  in  a  territory  lacking 
•easily  recognizable  marker  formations,  considerable  care  must  'be  exercised 
in  determining  the  final  point  for  excluding  top  water  and  in  selecting  the 
final  depth  to  drill  the  well. 

It  is,  of  course,  necessary  to  shut  off  low  enough  to  get  below  all  top 
water  and  to  stay  above  the  oil  sand.  There  is  considerable  leeway  for 
the  shut-off  point  at  El  Dorado,  as  a  number  of  tests  have  indicated  that 
there  is  no  water  nearer  than  about  100  feet  above  the  top  of  the  oil  sand. 

In  drilling  into  the  oil  formation,  it  is  important  to  use  great  care  (1) 
to  avoid  drilling  to  a  point  within  short  range  of  edge  water,  (2)  to  avoid 
drilling  into  bottom  water,  and  (3)  to  avoid  permanently  mudding  off  or 
seriously  injuring  low-pressure  oil  and  gas. 

If  it  is  known  that  in  certain  locations,  edge  water  lies  under  the  oil 
and  along  the  bottom  of  the  oil  sand,  the  hole  should  merely  penetrate  the 
top  of  the  sand  or  extend  into  the  sand  only  a  small  percentage  of  its  thick- 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 19 

ness.  In  this  way  considerable  oil  will  be  allowed  to  drain  laterally,  before 
the  water  can  overcome  friction  and  gravity  and  crowd  the  oil  back.  This 
means  of  conservation  fails  if  the  production  is  not  controlled  to  a  certain 
degree.  If  too  great  an  output  of  fluid  is  allowed,  the  water  will  soon  find 
its  way  into  the  well,  on  account  of  its  low  viscosity  (high  fluidity)  and  will 
"cone"  the  oil  back,  as  shown  in  Plate  IV.  Quite  a  number  of  El  Dorado 
wells  have  gone  to  water  prematurely  on  account  of  drilling  too  deep  into 
the  sand  or  by  not  sufficiently  restraining  production,  thereby  causing  the 
well  to  drill  itself  deeper  or  causing  the  water  from  below  to  be  sucked  up 
through  the  intervening  sand. 

The  term  "bottom  water"  is  here  used  to  mean  water  that  underlies 
the  oil  sand  and  is  separated  from  it  by  a  more  or  less  impervious  parting. 
Plate  IV  shows  the  apparent  relationship  of  the  oil  and  water.  Some  of  the 
wells  in  the  southern  portion  of  the  field  have  no  doubt  drilled  into  bottom 
water  on  account  of  finding  no  cap  above  the  oil  sand.  The  cap  at  the  bot- 
tom of  the  sand  was  sometimes  mistaken  for  the  cap  above  the  oil  sand 
and  the  well  was  drilled  into  bottom  water.  Sufficient  care  was  not  used 
in  determining  the  character  of  the  formation,  the  presence  of  oil  was  noted 
too  late  and  its  exact  source  was  misinterpreted.  Other  wells  have  been 
drilled  into  bottom  water  through  lack  of  proper  direction.  Much  of  that 
could  have  been  avoided  by  the  application  of  ordinary  engineering  meth- 
ods, which  allowed  conclusions  to  be  reached  from  a  study  based  largely 
on  the  data  of  neighboring  wells.  Full  consideration  should  be  given  to  the 
elevation  of  the  wells,  the  pitch  of  formation  in  different  directions  as 
shown  by  logs  (see  cross  sections  of  Plates  V  and  VI)  and  the  known  in- 
tervals between  marker  formations,  the  top  of  sand  and  bottom  water. 
Failure  to  consider  these  factors  has  cost  the  operators  dearly.  A  study 
of  the  well  logs  of  these  two  cross-sections  shows  that  in  most  cases  the 
oil  sand  is  the  principal  marker. 

Considerable  harm  is  likely  to  be  done  by  allowing  excessive  mud  and 
water  to  penetrate  low-pressure  oil  and  gas  strata.  When  the  formation  is 
not  very  porous,  it  may  be  better  to  plaster  it  up  with  thick  mud  and  avoid 
mudding  a  great  distance.  When  the  formation  is  quite  porous,  it  would 
appear  better  to  drill  in  with  water  rather  than  mud.  The  water  would 
be  more  readily  expelled  into  the  hole  again  and  would  act  as  a  less  effec- 
tive choke.  The  wells  of  El  Dorado  have  to  date  had  fairly  high  pressure 
with  which  to  free  themselves  of  rotary  mud.  Because  of  declining  gas  pres- 
sure, however,  future  Wells  will  not  clean  themselves  so  readily.  In  other 
fields,  wells  have  been  drilled  with  rotary  and  called  dry,  after  which  some 
of  the  formations  penetrated  have  been  proven  highly  productive.  There 
may  possibly  have  been  such  cases  in  the  El  Dorado  field  also. 

Certain  operators  report  that  there  is  little  opportunity  to  determine 
the  top  of  the  oil  sand  by  taking  core  barrel  samples  of  the  formations 
when  approaching  the  oil  sand,  on  account  of  the  incoherence  of  the  porous 
material.  The  writers  believe,  however,  that  too  little  attention  has  been 
given  to  core-barreling  in  El  Dorado,  because  such  work  has  been  very  suc- 
cessful in  other  fields  where  conditions  are  somewhat  similar. 

A  few  of  the  wells  have  been  finished  with  cable  tools  and  that  method 
is  more  satisfactory  than  the  rotary  tools,  for  the  following  reasons:  (1)  in 
order  to  pump  the  well,  it  must  be  partially  equipped  with  standard  cable 
tool  equipment  and,  therefore,  the  work  of  changing  the  rig  to  suit  cable 
tools  is  not  lost;  (2)  the  drilling  may  be  done  without  mud  and  usually 
with  much  less  fluid  in  the  hole;  (3)  running  the  bailer  to  clean  out  the 
drill  cuttings  gives  accurate  formation  samples  every  few  feet,  and  a  sam- 
ple can  be  obtained  at  any  depth  desired  with  little  delay.  In  some  fields 
with  loose  caving  oil  sand,  only  a  small  amount  of  open  hole  can  be  drilled 
in  cable  tool  work,  ahead  of  the  pipe,  but  at  El  Dorado  it  is  not  advisable 
to  drill  more  than  a  few  feet  into  the  oil  sand,  so  that  the  liner  can  be 
placed  with  cable  tool  equipment. 

Mr.  Winger,  who  initiated  the  finishing  of  wells  with  cable  tools  at 
El  Dorado,  has  communicated  the  following  information  on  the  rotary 
method  of  completing  wells: 

"In  drilling  with  a  rotary  it  is  frequently  impossible  to  determine  the 
exact  nature  of  the  formation  being  drilled,  for  the  reason  that  it  takes 
some  thirty  minutes  to  get  cuttings  from  the  bottom  of  a  2,000-foot  hole  and 


20 EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

there  is  also  good  opportunity  for  samples  being  mixtures  of  different  forma- 
tions. I  know  of  an  instance  in  this  field,  where  the  drillers  thought  they 
were' in  shale  and  decided  to  test  it  out  and  see  if  it  was  bearing  any  water. 
They  ran  the  bailer  four  or  five  times  and  the  well  came  in,  one  of  the  best 
in  the  field.  No  liner  had  been  set  or  other  necessary  preparations  made. 

"Another  instance:  A  certain  company  in  this  field  drilled  an  offset  to 
a  well,  the  sand  depth  of  which  was  known.  This  depth  was  reached,  but 
there  was  absolutely  no  showing — not  a  rainbow,  gas  bubble,  or  cutting  that 
indicated  anything.  But  the  neighboring  well  had  been  drilled  too  deep 
and  it  was  necessary  to  plug  back  to  shut  off  salt  water  before  making  a 
well  of  it.  So  this  company  stopped  there  where  the  "pay"  should  be  and 
after  bailing  about  twelve  hours  brought  in  their  well.  This  test  would 
not  have  been  made  at  that  point  had  they  not  known  the  exact  depth  to 
the  "pay"  in  their  neighbor's  well.  In  cable  tool  drilling,  the  cuttings  are 
brought  out  of  the  bottom  of  the  hole  each  time  with  the  bailer  and  there 
is  not  so  much  guess  work. 

"If  the  rig  is  standardized,  the  expensive  rotary  equipment  does  not 
have  to  remain  idle  ten  days  waiting  for  the  cement  to  set,  but  is  released 
to  another  location.  A  number  of  big  wells  in  this  field,  brought  in  by 
rotaries,  have  bridged  and  sanded  up  soon  after  the  machinery  was  moved 
off.  The  owners  lost  enough  production,  waiting  to  get  machinery  back  on 
the  well  to  clean  out,  to  pay  for  standardizing.  It  takes  several  days  to 
rig  up  a  rotary  and  get  it  back  on  the  job,  if  one  is  available,  whereas  if 
the  well  is  standardized  the  tools  and  sand  pump  can  be  run  and  production 
resumed  in  a  few  hours." 

The  operators  of  El  Dorado  who  have  tried  completing  wells  with  cable 
tools,  have  found  it  highly  satisfactory  and  express  their  intention  to  con- 
tinue the  practice. 

When  finishing  wells  with  cable  tools  in  high-pressure  territory,  it  is 
sometimes  necessary  to  use  care  in  removing  the  tools  from  the  hole,  lest 
the  well  blow  in.  The  "lubricator"  shown  in  Figure  1,  when  properly  used, 
will  prevent  blowouts.  In  at  least  one  instance  at  El  Dorado  it  was  used 
with  success.  Usually  a  short  string  of  drilling  tools  can  be  used  for  finish- 
ing, as  speed  is  not  so  necessary  at  this  place  in  the  work.  The  drilling  is 
done  through  the  control  head  (a)  and  the  master  gate  (k).  The  assembled 
lubricator  parts  (a),  (b)  and  (c)  are  hung  above  the  beam  with  the  drill- 
ing line  passing  through  them.  When  the  drilling  is  finished,  the  lubricator 
is  lowered  and  screwed  into  the  lower  control  head  (a).  The  upper  control 
head  (a)  and  oil  saver  (b)  are  then  closed  somewhat  on  the  line  and  the 
tools  are  pulled  up  to  the  position  shown.  The  master  gate  and  lower  con- 
trol head  can  then  be  closed,  the  lubricator  removed  and  preparations  made 
for  bringing  in  production. 

Although  careful  rotary  drilling  gives  good  results  in  many  instances, 
it  appears  certain  that  the  field  would  be  making  less  bottom  water  today 
if  all  of  the  wells  had  been  finished  with  cable  tools  in  the  hands  of  compe- 
tent drillers. 

There  is  probably  not  a  well  in  the  El  Dorado  field  that  has  used  a  full 
oil  string  for  producing.  Perforated  liners  or  screen  pipe  or  a  combination 
of  both  are  generally  used.  The  loose  sand  problem  is  difficult  of  solution 
and  greatly  retards  production.  It  will  be  discussed  under  "Production 
methods." 

Labor  Conditions: 

The  nation-wide  rush  for  oil,  with  high  prices  for  oil,  which  was 
initiated  by  the  demands  of  the  World  War,  resulted  in  much  wildcatting 
and  the  opening  of  many  new  fields.  In  order  to  handle  the  vast  amount 
of  work,  it  was  necessary  that  men  with  little  oil  field  experience  be  en- 
trusted with  important  phases  of  development  and  production.  A  compe- 
tent oil  man  cannot  be  developed  in  a  few  months  or  even  years,  and  hence 
tnere  has  been  much  mismanagement  and  poor  workmanship.  The  El 
Dorado  field  has  suffered  considerably  from  this  condition,  which  probably 
cannot  be  righted  for  some  time. 

The  following  example  of  poor  handling  was  furnished  by  a  driller  fami- 
liar with  the  work  on  the  particular  well:  A  well  was  drilled  with  rotary 
tools  to  the  depth  estimated  from  the  logs  of  neighboring  wells,  as  sufficient 
to  encounter  the  oil  sand.  The  mud  was  thinned  considerably  and  a  show 
of  gas  appeared.  Without  thickening  the  muddy  water  and  without  keep- 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


21 


LEGEND 

a     Control  Head 
b     Oil  Saver 
c     Two  Joints  6"  Pipe 
d     Valve  5terr, 

Flow  Line 

Bull   Pluc, 

Clamps  On  e"PTpe 

Clamps  On  10"  -Pioe 
Tools 

Master  Gate 
10'  Pipe 
Valve  Wnsncb 


FIGURE! 


Fig.  1.     Cable  Tool   Lubricator  for  High   Pressure  Walls. 


22 EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

ing  the  hole  full  of  fluid,  the  drill  stem  was  withdrawn  from  the  hole  as 
rapidly  as  possible.  The  driller  stated  that  this  was  done  in  order  to  get 
the  casing  in  as  soon  as  possible.  The  removal  of  the  drill  stem  lowered 
the  fluid  in  the  hole  and  the  well  blew  out  before  the  drill  stem  was  with- 
drawn. About  1,300  feet  of  drill  pipe  was  dropped  to  the  bottom.  The  wild 
flow  either  drilled  the  well  into  bottom  water  or  sucked  up  edge  water  and 
the  production  turned  largely  to  water.  The  fluid  ran  into  earthen  sumps 
and  much  of  the  oil  produced  was  lost  in  spray,  evaporation  and  seepage. 
It  becomes  difficult  to  repair  such  a  well  on  account  of  the  large  cavities 
formed  by  blowing  out  sand  and  on  account  of  the  damage  done  to  thin  im- 
pervious partings  that  may  exist  'between  the  oil  and  water.  This  well  was 
ruined  by  improper  handling  and  in  addition  to  the  loss  of  the  hole  and  re- 
sultant expense  it  has,  no  doubt,  done  great  damage  to  the  surrounding  ter- 
ritory. 

Drilling  Costs: 

The  majority  of  the  wells  at  El  Dorado  have  been  drilled  by  con- 
tractors. On  account  of  easy  drilling,  the  wells  are  completed  at  approx- 
imately 2,200  feet  in  about  thirty  days.  Some  of  the  first  contracts  called 
for  a  completion  of  the  well,  ready  to  flow,  for  $25,000.  These  were  known 
as  "turn-key"  jobs.  Since  labor  and  material  have  become  cheaper,  and. 
more  competition  has  entered  into  contracting,  the  price  has  been  reduced 
to  about  $12,000  or  about  $5.50  per  foot.  One  operating  company  reports 
considerable  saving  by  drilling  their  own  wells.  Using  $5.50  as  the  con- 
tract basis,  it  is  stated  that  a  saving  of  from  $0.59  to  $3.90  per  foot  has  been 
accomplished.  These  figures  represent  a  total  saving  range  of  $1,300  and 
$8,490  per  well,  respectively.  The  average  reported  saving  was  $2.81  per 
foot.  The  cost  for  200  feet  of  10-inch  and  2,100  feet  of  6-inch  8-thread  line 
pipe  is  at  present  (November.  1921)  about  $3,000.  The  contract  price  for 
a  112-foot  rotary  derrick  is  $800.  The  cost  of  derrick  and  combination  rig 
(rotary  timbering  and  standard  rig  irons  and  wheels)  is  about  $1,500.  The 
cost  of  casing  and  rotary  derrick  is  included  in  the  $12,000  for  a  "turn-key" 
job. 

The  prevailing  wages  for  rotary  crews  in  October,  1921,  was  $10  per 
12-hour  period  for  drillers  and  $5  each  for  the  remainder  of  the  well  crew. 


Water  Conditions 


Amount  of  Water  Produced: 

The  amount  of  water  produced  in  the  Ed  Dorado  field  is  difficult  to 
approximate,  because  of  the  failure  of  operators  to  gauge  the  water  produc- 
tion as  a  whole  or  from  individual  wells.  A  large  proportion  of  the  water 
produced  is  bled  from  the  separators  as  free  water.  As  the  water  comes 
from  the  bleeder  lines  through  "cracked"  valves,  it  is  under  considerable 
pressure  and  is,  therefore,  in  the  form  of  small  high-velocity  streams  and 
spray,  rendering  estimation  very  uncertain.  Much  water  escapes  by  run- 
ning into  streams  and  sinking  into  the  ground. 

A  large  proportion  of  the  water  from  numerous  wells  passes  into  the 
first  storage  tanks  as  emulsions.  After  this  emulsion  is  broken  up  by  spe- 
cial treatment,  the  amount  of  water  present  is  not  usually  measured. 

Estimates  of  total  water  production  by  those  familiar  with  field  condi- 
tions, range  from  25  to  50  per  cent  of  the  total  fluid  raised.  Operators  who 
are  more  familiar  with  conditions  in  the  north  end  of  the  field  are  apt  to 
under-estimate  the  water  production,  while  those  of  mostly  south-end  ex- 
perience are  likely  to  over-estimate  it. 

It  is  believed  by  the  writers  that  at  least  one-third  of  the  gross  produc- 
tion in  October,  1921,  was  water.     At  any  rate,  the  amount  of  water  being 
recovered  with  the  oil  is  enough  to  cause  serious  alarm  concerning  the  life 
of  the  field. 
Harmful   Effects  of  Water: 

The  very  rapid  decline  of  production  in  this  field  is  no  doubt  caused  by 
water,  more  than  by  any  other  factor.  All  operators  of  wide  experience  with 
production  of  this  character  realize  the  harmful  effects  of  water  under  cer- 
tain conditions,  and  so  much  has  been  written  on  the  subject  that  only  gen- 
eral references  are  given  to  some  publications  of  the  U.  S.  Bureau  of 
Mines.* 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 23. 

The  physical  properties  of  oil  and  water  are  widely  different.  Water 
is  considerably  heavier  than  El  Dorado  oil,  is  more  fluid  (less  viscous)  at 
ordinary  temperatures,  and  has  greater  surface  tension.  Each  of  these 
characteristics  of  water  gives  it  an  advantage  over  oil  when  the  two  liquids 
are  competing  for  passage  through  the  reservoir  rocks  toward  the  wells. 
Water  is  also  very  effective  in  "killing"  gas  action,  especially  when  the 
sediments  are  of  close  texture. 

The  weight  of  water  standing  in  a  well  exerts  a  hack-pressure  on  the 
oil  in  the  formations  and  tends  to  hold  it  there.  When  oil  once  reaches 
the  well  there  is,  of  course,  nothing  to  prevent  it  from  rising  to  the  top  of 
the  fluid  column,  it  being  lighter  than  water. 

Viscosities  of  liquids  are  measured  by  means  of  a  viscosimeter,  and 
this  instrument  demonstrates  that  water  is  more  fluid  than  oil.  For  the 
benefit  of  the  field  man,  a  brief  description  is  given.  It  is  essentially  a  tall 
cylindrical  vessel  with  a  small  standard  spout  opening  in  the  side  at  the 
bottom.  The  viscosity  of  liquids  are  compared  by  the  time  it  takes  to 
empty  the  vessel  through  the  orifice.  It  is  thus  shown  that  water  will  move 
through  small  openings  much  more  freely  than  will  oil. 

If  water  and  oil  are  present  in  a  stratum  penetrated  by  a  well,  although 
the  water  will  occupy  the  bottom  portion,  drilling  too  deep  or  removing 
the  fluid  too  rapidly,  will  allow  the  water  to  rush  into  the  well  and  crowd  at 
least  some  of  the  oil  back.  Gas  pressure  is,  in  general,  the  principal  force 
that  carries  oil  toward  a  well,  the  force  of  gravity  being  of  only  minor  im- 
portance, especially  in  strata  of  low  inclination  and  small  thickness.  Ex- 
cessive water  will  reduce  or  "drown  out"  all  but  high-pressure  gas  with  dis- 
astrous effects  on  production. 

Water  has  greater  surface  tension  and  is  attracted  more  strongly  by 
the  formations  than  is  oil.  The  force,  known  as  capillary  attraction  will 
draw  water  upward  in  much  the  same  way  that  a  wick  supplies  oil  to  a 
flame.  The  water  tends  to  "grip"  the  formation  particles  and  thereby  re- 
tards the  movement  of  oil  and  gas.  That  force  is  strongest  in  fine-grained 
material  or  in  minute  crevices  and  the  greatest  retardation  of  movement  by 
water  can,  therefore,  prevail  in  such  material.  As  an  illustration,  consider 
two  sands  that  are  each  composed  of  spherical  grains.  The  grains  of  sand 
A  have  a  diameter  of  .005  inch,  while  those  of  sand  B  measure  .050  inch,  or 
ten  times  greater.  Each  sand  has  the  same  percentage  porosity  and  will 
hold  the  same  amount  of  fluid.  Movement  can  occur  more  easily  in  B  than 
in  A,  because  there  is  less  frictional  resistance  and  less  capillarity  on 
account  of  the  larger  space  between  the  .grains. 

Source  of  Water: 

There  is  little  doubt  that  over  90  per  cent  of  the  water  produced  at 
El  Dorado  is  a  combination  of  bottom  water,  which  underlies  the  oil-bearing 
strata  and  appears  to  be  uniformly  separated  from  it  by  a  cap  rock,  and" 
edge  water  which  is  present  in  the  down-dip  and  lower  portion  of  the  oil- 
bearing  strata. 

It  is  not  unlikely  that  some  faulty  shut-offs  are  letting  in  top  water,  but 
from  the  data  at  hand  this  source  appears  insignificant.  The  minimum  re- 
quirements of  the  Conservation  Commission  for  water  strings,  are  twenty- 
five  sacks  of  cement  to  set  thirty-six  hours  for  170  feet  of  shallow  string 
and  sixty  sacks  of  cement  to  set  ten  days  in  the  case  of  the  final  string, 
which  is  usually  6-inch  19%-pounds  pipe.  A  test  of  water  shut-off  is  re- 
quired on  the  main  water  string.  If  the  test  is  not  satisfactory,  the  condi- 
tion must  be  remedied  before  drilling  into  the  oil.  The  operator  should  be 
more  anxious  to  exclude  the  water  than  any  one  else,  but  as  he  cannot  always 
be  present  at  such  tests,  the  responsibility  may  be  left  with  the  foreman, 
driller  or  contractor,  who  is  often  careless  about  such  work.  It  would  be 
desirable  for  a  Conservation  Commission  officer  to  witness  all  tests  for 


^Bulletin  No.  134,  The  Use  of  Mud-Laden  Fluid  in  Oil  and  Gas  Wells,  by 
J.  O.  Lewis  and  W.  F.  McMurray,  1916. 

^Bulletin  No.  163,  Methods  of  Shutting  Off  Water  in  Oil  and  Gas  Wells,  by 
F.  B.  Tough,  1918. 

*Bulletin  No.  195,  Underground  Conditions  in  Oil  Fields,  by  A.  W.  Am- 
brose, 1921. 


24  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

water  shut-offs.  The  results  of  each  test  could  then  be  reported  and  an 
adequate  record  kept  by  both  the  operator  and  the  Commission,  which  would 
be  of  value  in  future  work. 

A  number  of  circumstances  may  arise  that  cause  water  shut-offs  to  leak. 
They  will  be  mentioned  as  of  possible  value  in  determining  upon  the  source 
of  water  in  this  field: 

(1) — Running  casing  in  hole  may  loosen  threads  and  cause  leaks.  This 
is  not  so  apt  to  happen  with  mud  back  of  the  casing  as  with  water.  Often- 
times, casing  is  not  screwed  up  tightly  and  by  putting  on  tongs  and  screw- 
ing up,  the  water  may  be  shut  out.  Source  of  leak  can  be  determined  by 
running  casing  tester  or  by  setting  a  packer  on  tubing.  Before  drilling  out 
cement  for  test  of  shut-off,  the  tightness  of  the  casing  itself  should  be  ascer- 
tained by  bailing  out  the  mud  or  water  and  letting  the  well  stand  undis- 
turbed for  about  five  hours.  If  nothing  collects  in  the  bottom,  other  than 
that  reasonably  expected  as  drain-back,  the  casing  may  be  considered  tight. 
If  a  large  quantity  of  cement  has  been  used  and  a  large  proportion  of  it 
sets  inside  the  casing,  it  may  become  necessary  to  test  the  lower  portion 
of  the  casing  after  the  cement  is  drilled  out. 

(2) — Casing  may  be  imperfect  in  places  or  may  develop  breaks  while 
running  in.  If  second-hand  pipe  is  used  in  high-pressure  territory,  it  is  well 
to  test  each  joint  with  hydraulic  pressure  before  using.  In  the  Monroe, 
Louisiana,  gas  field  some  of  the  operators  test  their  casing  and  fittings  with 
a  special  apparatus.  A  description  and  photograph  of  such  apparatus  can 
be  found  in  Bulletin  No.  9  (pp.  55.  56)  of  the  State  of  Louisiana,  Depart- 
ment of  Conservation,  a  co-operative  report  written  by  H.  W.  Bell  and  R.  A. 
Cattell  of  the  Bureau  of  Mines.  In  testing  one  string  of  6-inch,  19%-pound 
pipe,  at  the  factory,  twenty  out  of  the  sixty  joints  leaked,  and  one  joint 
split  about  fifteen  inches  on  one  end  under  an  internal  pressure  of  less  than 
1,200  pounds  per  square  inch. 

(3) — After  determining  that  the  casing  does  not  leak,  the  cement  should 
be  drilled  out  and  the  well  drilled  to  the  formation  in  place.  For  safety, 
drilling  should  be  stopped  when  about  one  foot  into  the  formation.  If  a  new 
water  or  oil  and  gas  stratum  is  encountered  at  the  shoe,  it  will  be  impos- 
sible to  test  the  effectiveness  of  the  shut-off. 

(4) — After  drilling  out  cement  and  bailing  down  for  test,  drilling  mud 
and  water  may  rise  to  a  high  level,  due  to  being  returned  from  porous  for- 
mations adjacent  to  the  shoe.  Indeed,  it  may  require  a  number  of  tests  to 
show  that  such  inflow  is  decreasing  and  is  exhaustible  and  that  the  cement- 
ing operation  was  a  success. 

(5) — If  too  much  hole  is  made  for  the  test  and  new  water  is  encoun- 
tered below,  that  fact  may  not  be  recognized  until  after  considerable  work 
is  done.  The  shoe  may  be  in  the  middle  of  a  water-bearing  formation,  a 
very  short  distance  above  it,  or  a  considerable  distance  above  it.  In  the 
first  case,  it  may  be  impossible  to  demonstrate  the  source.  In  rotary  wells 
it  should,  in  all  cases,  be  noted  whether  mud  is  coming  in,  and  in  every 
case  whether  known  upper  deposits  are  supplying  oil  or  gas  around  the 
shoes.  If  a  good  dye  is  placed  behind  the  water  string  and  shows  up  at 
the  shoe,  the  test  indicates  the  water  string  is  leaking,  but  if  it  does  not 
appear,  nothing  is  proved.  In  the  second  case,  it  may  not  be  possible  to  set 
a  cement  or  other  plug  to  exclude  the  water  from  below  and,  at  the  same 
time,  leave  a  little  open  space  below  the  shoe.  If  the  dye  test  fails,  the 
source  might  be  proven,  as  has  been  done  elsewhere,  by  plugging  the  forma- 
tion with  cement  and  up  to  about  two  feet  into  the  shoe;  then  perforating 
the  water  string  a  few  feet  above  the  shoe,  until  formation  comes  in.  The 
kind  and  amount  of  fluid  that  enters  will  probably  indicate  the  source  of 
water.  It  is  a  dangerous  thing,  however,  to  punch  holes  in  a  water  string 
and  this  should  be  done  only  as  a  last  resort.  In  the  third  case,  the 
source  could  be  demonstrated  by  placing  a  cement  bridge  just  below  the 
shoe  or  possibly  by  setting  a  packer  in  formation  just  below  the  shoe,  and 
making  a  bailing  test. 

In  some  fields,  where  cable  tools  are  used  samples  of  each  water  en- 
countered, or  at  least  a  composite  sample  of  all  top  water,  are  obtained 
and  analyzed.  In  this  way  the  source  of  water  is  usually  easily  deter- 
minable  by  comparison  with  the  analysis  of  water  in  question,  as  the 
chemical  characteristics  of  the  mineral  content  of  oil-field  water  usually 
change  considerably  with  depth.  A  comparison  of  fluid  levels  and  of 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  25 

amounts  of  the  known  and  unknown  water  is  often  sufficient  evidence  of 
the  source.  With  rotary  drilling,  these  methods  are  impossible,  except  in 
rare  cases'. 

(6) — Besides  making  sure  that  the  cement  has  been  drilled  through 
for  a  test,  no  shut-off  should  be  passed  unless  the  hole  can  be  kept  cleaned 
out  to  bottom.  Heaving  formation  may  bridge  and  hold  back  water. 

(7) — In  drilling  out  a  considerable  distance  below  the  shoe  of  a  water 
string,  oil-bearing  formations  may  be  penetrated  or  re-exposed  and  the  test 
of  shut-off  thereby  rendered  more  difficult  or  inconclusive,  due  to  the  oil 
or  gas  coming  into  the  hole.  In  such  cases,  it  is  usually  not  possible  to 
plug  off  the  oil  or  gas  without  also  sealing  the  shoe  of  the  water  string. 
The  only  recourse  then  is  to  make  a  production  test  in  an  effort  to  de- 
termine the  condition  of  the  shut-off,  either  by  producing  from  present 
depth  or  after  deepening  for  more  production.  The  former  method,  that 
is,  before  deepeneing,  is  more  reliable  because  deeper  drilling  may  en- 
counter lower  water.  Obv-iously,  the  production  test  is  not  conclusive 
unless  the  well  settles  down  to  a  clean  production  and  it  should,  therp- 
fore,  be  avoided,  except  as  a  last  resort. 

The  liability  of  error  in  measuring  the  depth  of  the  shoe  is  believed 
by  some  to  be  sufficient  reason  for  drilling  out  an  excessive  amount  below 
the  shoe.  However,  there  is  no  call  for  such  procedure  if  broken  cement 
and  formation  are  brought  to  the  surface. 

In  general,  the  determination  of  the  source  of  water  in  a  well  or 
group  of  wells,  can  be  indicated  by  the  use  of  the  following: 

(1) — Formation,  production  and  casing  records  of  wells. 

(2) — Graphic  means  to  visualize  complex  data. 

(3) — Comparison  of  physical  characteristics  of  water  produced. 

(4) — Amounts  of  water  producible  by  wells. 

(5) — Comparison  of  fluid  levels. 

(6) — Bridges   and   plugs  of  cement  or  other  impervious   material. 

(7) — Dyes  or  colorless  substances  for  tracing  underground  flow  of 
water. 

(8) — Packers  used  in  casing  or  in  formation. 

(9) — Muddy  water  to  indicate  point  of  entry. 

(10) — Relation  of  sequence  of  wells  "going  to  water"  to  geologic 
structure. 

(11) — Comparison  of  chemical  analyses  of  waters. 

(12) — Oil  and  emulsions  accompanying  water. 

When  water  appears  after  a  well  has  been  producing  clean  oil,  it  is 
usually  more  difficult  to  determine  its  source  than  at  the  time  of  a  test 
of  shut-off,  because  the  possible  sources  of  the  water  have  increased.  It 
is  one  thing  to  determine  through  what  channel  or  stratum  water  is  en- 
tering a  well,  and  another  to  ascertain  how  the  water  came  to  be  in 
that  particular  stratum.  When  water  is  native  to  a  certain  stratum,  it 
is  here  called  "primary  water;"  when  it  obtains  access  through  the 
agency  of  a  well,  to  other  formations,  it  is  termed  "secondary  water"  with 
respect  to  those  formations.  The  waters  of  the  typical  oil  field  can  be 
classified  with  respect  to  position  under  the  three  headings,  upper,  lower 
and  intermediate  water.  It  is,  therefore,  possible,  in  general,  that  water 
found  in  production  may  be  from  either  of  these  sources  and  may  be  pri- 
mary or  secondary  in  character.  The  possible  contributory  combinations 
of  these  six  elements  are  many.  In  dealing  with  water  conditions  in  a 
group  of  wells,  all  of  these  possibilities  may  demand  consideration.  The 
problem  is  probably  best  attacked  by  first  paying  attention  to  the  wells 
producing  most  water  and  having  the  highest  fluid  levels.  In  order  to 
make  reliable  comparison,  each  pumping  well  should  be  tubed  near  the 
bottom  and  the  lifting  of  the'  fluid  conducted  under  similar  conditions.  It 
is  safe  to  assume  at  the  start  and  in  the  absence  of  more  convincing  data, 
that  the  largest  water  producers,  or  the  wells  with  highest  fluid  levels,  are 
the  offenders. 

An  outline  is  given  of  the  various  means  of  determining  the  source 
of  water  in  oil  and  gas  wells.  In  dealing  with  this  phase  of  the  subject, 
general  material  was  drawn  from  a  paper  entitled  "Source  of  Water  in  Oil 
Wells,"  which  was  written  by  the  senior  author  and  appeared  in  the  Feb- 
ruary, 1920,  issue  of  "Summary  of  Operations"  of  the  California  State 
Mining  Bureau. 


26  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

(1) — Formation,  Production  and  Casino   Records  of  Wells: 

In  order  to  save  time  and  money  in  dealing  with  water  problems,  it  is 
necessary  to  assemble  accurate  and  exhaustive  data  on  each  well  and  to 
record  these  in  convenient  and  readable  form.  Those  in  authority  should 
standardize  as  far  as  practicable  for  a  given  area  the  nomenclature  of  for- 
mations encountered  in  drilling.  It  is  desirable  that  the  driller's  designa- 
tion of  samples  should  be  confirmed  before  the  final  log  is  made.  With  one 
person  determining  all  samples  from  several  drilling  wells  on  a  property, 
uniformity  of  formation  names  can  be  accomplished.  For  instance,  drillers 
in  the  same  field  often  name  the  same  formation  differently.  Some  samples 
which  are  inspected  with  different  degrees  of  scrutiny  and  under  vary- 
ing conditions  of  moisture,  light,  etc.,  may  give  diverse  impressions  to 
different  people. 

Without  a  uniform  system  of  logging  formations,  it  is,  in  the  absence 
of  unmistakable  markers,  difficult  to  correlate  the  well  logs.  Errors  in 
correlation  lead  to  incorrect  methods  of  combating  water  troubles,  and  also 
to  non-uniform  water  shut-offs.  By  this  means,  top  water  behind  a  water 
string  may  be  allowed  to  enter  any  porous  formation  and  travel  through 
this  channel  to  a  nearby  well  in  which  this  porous  formation  is  exposed 
in  the  hole. 

There  is,  as  yet,  no  evidence  that  non-uniform  shut-offs  are  responsible 
for  any  water  production  at  El  Dorado.  Such  is  not  likely  to  be  the  case, 
if  the  cement  used  has  properly  bonded  with  the  casing  and  walls  of  the 
hole,  for  100  feet  or  so,  above  the  shoes  of  the  water  strings. 

The  need  for  accurate  figures  for  production  of  oil  and  water  is  too 
often  overlooked.  Erroneous  ideas  concerning  the  source  of  water  in  pro- 
duction are  likely  to  be  developed  to  the  end  of  misdirected  remedial 
effort.  This  is  particularly  true  when  two  or  more  wells  produce  into  the 
same  tank.  Suitable  equipment  for  the  accurate  determination  of  amounts 
of  oil,  water  and  emulsion  produced  by  each  well  will  be  found  a  sound 
business  investment  in  many  cases. 

Full  records  of  all  casing  put  into  and  removed  from  each  well  should 
be  available  for  use  in  case  of  water  troubles  or  abandonment.  The  amount 
and  location  of  any  side-tracked  and  perforated  casing  should  also  be  re- 
corded. Side-tracked  casing  may  be  left  in  such  a  position  and  condition 
as  to  afford  a  passageway  for  water  down  past  a  shut-off  point  or  upward 
past  a  plug  or  bridge,  and  thus  prevent  a  determination  of  the  true  source 
of  the  water. 

(2) — Graphic  Means  to  Visualize  Complex  Data: 

In  dealing  with  oil  field  problems,  it  is  important  to  know  the  under- 
ground structure  and  to  obtain  all  possible  information  relative  to  the  oc- 
currence and  production  of  oil,  gas  and  water.  Ambrose*  has  pointed  out 
that  the  best  use  of  field  data  can  be  made  when  presented  in  graphic 
form,  by  cross  sections,  underground  contour  maps,  production  curves  and 
peg  models. 

Until  the  geologic  structure  is  accurately  known,  it  will  not  be  ap- 
parent where  to  make  the  water  shut-offs  in  order  to  establish  a  strati- 
graphic  uniformity.  Peg  models  and  cross-sections  are  used  especially  to 
determine  structure  and  to  indicate  sources  of  water  due  to  haphazard 
drilling  campaigns. 

With  the  aid  of  models  and  sections,  the  location  of  water  that  may 
lie  in  or  below  the  oil  measures  can  also  be  determined  with  more  or  less 
accuracy  and  drilling  governed  accordingly. 

The  comparison  of  the  behavior  of  neighboring  wells  often  gives  cri- 
teria regarding  underground  connections  and  source  of  water.  Charts  that 
show  graphically  the  average  daily  amounts  of  oil  and  water  produced  by 
each  well  during  each  month,  and  the  number  of  days  the  well  produced 
during  the  month,  together  with  the  reasons _  for  anv  non-producing  days, 
are  valuable  to  indicate  the  effect  of  certain  conditions  or  operations  at 
one  well  upon  the  production  of  another. 

In  considering  the  data  of  more  than  two  wells,  the  problem  becomes 
complicated  and  graphical  representation  of  data  is  necessary,  in  order  to 
make  a  reliable  study  of  the  several  features,  such  as  time  and  volume 
of  producible  water. 


*Afnbrose,    Undcriiroiuid   Conditions   in    Oil   !:ii'lds.    liuU.    /Q.I    I".   S.    H urea  it 
Mines,  .^.  >6-fiS. 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 


(3) — Comparison    of   Physical   Characteristics   of   Water: 

The  easily  distinguishable  non-chemical  properties  of  water,  such  as 
taste,  temperature  and  odor,  are  often  serviceable  in  indicating  source  of 
water  entering  a  well.  If  one  or  more  of  these  properties  are  known 
for  the  different  waters  encountered  in  drilling  a  well,  an  idea  of  the 
source  of  the  water  appearing  in  production  can  sometimes  be  had.  It  '"s 
usually  not  practicable  to  observe  these  conditions,  due  to  the  contamina- 
tion of  added  water,  or  of  new  water  encountered  in  the  well,  or  due  to 
rotary  drilling.  However,  it  is  well  to  note,  when  possible,  the  taste. 
Temperature  and  odor  of  first  water  or  its  resultant  combination  with 
other  waters  cased  off  behind  a  water  string.  The  value  of  this  feature 
is  greater  when  the  well  is  drilled  "dry"  with  cable  tools  or  when  no 
drilling  water  whatever  has  to  be  added  from  the  surface. 

Ordinarily,  the  hotter  water  comes  from  the  deeper  levels.  Water  that 
is  salty  to  the  taste  usually  comes  from  deeper  levels  than  fresher  water. 
Sulphur  gas  is  the  principal  source  of  odor  in  water,  and  its  presence  can 
be  substantiated  by  its  blackening  effect  on  silver.  The  writers  have  not 
noticed  any  sulphur  water  at  El  Dorado. 

Although  such  observations  for  a  particular  well  may  indicate  that  tlie 
well  is  making  top  water,  it  would'  remain  to  determine  whether  top 
water  was  entering  the  productive  formations  as  a  result  of  the  faulty 
condition  of  some  other  well.  Similarly,  it  should  be  determined  whether 
any  supposed  lower  water  was  of  secondary  origin. 

(4) — Amounts  of  Water  Produced   by  Wells: 

The  terms  "amount"  and  "quantity"  used  here  refer  To  actual  volume 
rather  than  percentages.  Often  in  groups  of  producing  wells,  the  well 
which  makes  the  most  water  can  be  singled  out  as  the  probable  offender. 
This  is  true  of  pumping  wells  when  they  produce  all  of  the  fluid  that 
comes  into  the  hole. 

Stratigraphically  non-uniform  shut-offs  may  make  it  difficult  to  des- 
ignate the  well  letting  water  into  the  oil  sand.  Due  to  a  low  shut-off,  well 
Xo.  1  may  allow  considerable  top  water  to  infiltrate  into  the  production 
of  well  No.  2.  Well  No.  2  may  thereby  become  the  largest  water  producer 
of  a  group  of  wells,  but  could  not  rightly  be  called  the  offending  well.  On 
the  other  hand,  well  No.  1  may  produce  the  least  water  of  the  group  and 
its  status  would  have  to  be  determined  by  other  means. 

The  amounts  of  water  produced  by  pumping  wells  are  of  little  sig- 
nificance in  indicating  the  source  of  water  when  the  fluid  levels  are  con- 
Tinually  and  uniformly  high.  In  such  cases,  the  productions  do  not  rep- 
resent the  fluid  capacities  of  the  wells  and  the  amounts  of  production  ob- 
viously depend  then  on  such  features  as  size  of  pump  and  tubing,  efficiency 
of  pump,  length  of  stroke  and  number  of  strokes  per  minute.  It  is  evident 
that  under  such  conditions  the  offending  wells  may  be  producing  less 
water  than  a  well  or  wells  not  letting  water  into  the  sand. 

An  increace  or  decrease  in  the  amount  of  water  a  well  produces  is 
an  important  item  to  consider  for  indicating  the  source  of  the  water.  The 
sudden  appearance  of  considerable  water  in  a  well  or  wells  would  indi- 
cate possible  sources,  and  these  would  be  dependent  largely  on  the  con- 
ditions obtaining  in  that  area.  Under  average  conditions  such  a  sudden 
increase  of  water  would  appear. more  likely  to  be  due  to  causes  imme- 
diately connected  with  the  well  itself. 

A  sudden  increase  in  water  production  would  point  to  such  things  as 
a  sudden  development  of  large  casing  leak;  the  failure  of  shut-off;  the 
breaking  in  of  water  through  thin  formation  or  past  a  plug  in  the  bot- 
tom of  the  well;  or  the  water  pressure  overcoming  the  effect  of  oil  and 
gas  pressure.  It  is  quite  possible  also  that  edge  watrr  or  water  due  to 
the  drilling  or  to  the  fault  of  some  other  producing  well,  could  manifest 
itself  suddenly  when  conditions  of  porosity  are  i'avorable. 

After  conditions  have  been  remedied  in  the  well  in  question,  or  in 
neighboring  wells,  it  may  require  considerable  time  to  exhaust  the  accu- 
mulated secondary  water  from  the  formations.  The  rate  of  exhaustion 
would,  of  course,  depend  again  on  the  porosity  of  exposed  strata.  A 
aradual  decrease  in  amount  would  indicate  that  the  water  was  lej:  into 
the  sand,  and  not  native  to  it. 


28  EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

(5) — Comparison   of   Fluid    Levels: 

Fluid  levels  may  be   classified  as   follows: 

(1) — Those   compared    on   a   basis    of    distance   from    sea   l?vel    will   be 

termed  "absolute." 
(2)     Those  compared   with  reference  to  distance  from  a  stratigraphic 

horizon  or  stratum  will  be  termed  "stratigraphic." 

High  fluid  levels  usually  indicate  large  productive  possibilities  of  oil 
or  water.  They  also  indicate  the  offending  wells  when  the  fluid  level  is 
due  to  an  excess  of  water.  It  is  out  of  the  ordinary  to  find  a  condition, 
for  a  group  of  wells  with  settled  production  that  have 'gone  to  water, 
whereby  the  offending  wells  would  not  show  the  highest  fluid  levels.  This 
is  noticeable  in  several  cases  at  El  Dorado.  Exceptions  to  this  general 
rule  are  found  when  water  is  entering  the  lower  portion  of  a  well  and  is 
restrained  from  seeking  its  own  level  in  that  well  by  a  bridge  or  by  a 
plug,  the  lower  portion  of  which  was  defective.  In  such  cases,  the  con- 
fined water  will  travel  across  to  other  wells  through  any  porous  strata 
available.  In  an  area  of  markedly  inclined  strata;  water  which  enters  a 
well  at  any  point  may  be  conducted  rapidly  away  by  an  unsaturated  or 
partially  drained  porous  stratum  to  another  well^  and  the  conditions  of 
porosity  may  be  such  that  the  secondary  water  will  attain  a  higher  strati- 
graphic  fluid  level  in  the  down-dip  well. 

The  fluid  levels  should  be  taken,  when  possible,  for  idle  as  well  as 
for  producing  wells.  It  is,  of  course,  necessary  to  obtain  these 
data  under  similar  conditions  for  the  different  producing  wells. 
The  levels  should  be  taken  at  a  certain  time  after  produc- 
tion was  stopped.  It  is  also  advisable  to  conduct  an  investigation  of 
fluid  levels  after  a  period  of  uniform  producing  conditions  for  all  wells 
has  elapsed.  If  a  well  has  been  pumping  only  a  few  days  after  a  con- 
siderable period  of  idleness,  the  figure  obtained  may  be  misleading.  It  is 
apparent  that  an  idle  well  will  probably  have  a  high  fluid  level.  If  its 
level  is  considerably  higher  than  those  of  neighboring  wells,  it  should  be 
made  the  object  of  further  investigation  as,  under  ordinary  circumstances, 
such  a  condition  could  not  exist  in  a  non-offending  well. 

A  comparison  of  fluid  levels  should  be  considered  on  the  same  strati- 
sraphic  plane,  although  if  the  formations  have  a  gentle  dip,  sea  level 
basis  will  usually  suffice.  The  greater  the  resistance  to  the  passage  of 
water  from  one  well  to  another,  the  greater  will  be  the  difference  in  fluid 
levels  of  the  offending  and  non-offending  wells. 

When  infiltrating  water  travels  up  the  dip  of  fairly  steeply  inclined 
beds,  a  stratigraphic  comparison  of  fluid  levels  will  tend  to  exaggerate 
the  comparison,  because  the  up-dip  non-offending  well  could  never  attain 
the  same  stratigraphic  fluid  level,  due  to  water  pressure,  as  the  offending 
down-dip  well.  The  opposite  is,  of  course,  true  when  the  water  travels 
down  the  dip. 

It  is  felt  that  the  operators  in  El  Dorado  have  not  studied  fluid  levels 
to  the  extent  that  should  be  done  and  it  is  believed  that  such  a  study 
would  often  be  helpful  in  determining  the  repair  of  wells.  The  preceding 
data  on  fluid  levels  was  given  in  considerable  detail  in  the  hope  that 
such  information  might  be  useful  in  later  work  in  this  field. 

(6) — Bridges   and    Plugs  of   Cement   or   Other   Impervious    Material: 

Ihe  terms  "bridge"  and  "plugs"  are  sometimes  used  synonymously. 
"Bridge"  is  here  used  when  the  impervious  filling  is  not  in  contact  with 
the  bottom  of  the  well;  while  "plug"  designates  a  filling,  part  of  which  is 
imnervious,  which  is  in  contact  with  the  formation  at.  the  bottom  of  the 
well. 

The  proper  manipulation  of  bridges  and  plugs  of  cement  is  frequently 
employed  and  is  one  of  the  most  reliable  means  of  determining  source 
of  water.  If  plugging  the  bottom  of  the  hole  shows  that  the  water  has 
been  entering  the  well  at  that  point,  the  demonstration  may  constitute 
the  remedy. 

If  a  studv  of  all  available  information  does  not  sufficiently  indicate  the 
point  of  entry  of  water  in  a  well,  the  following  is  a  proposed  outline  of 
work: 

(a) — Retest  the  shut-off  by  placing  a  substantial  cement  bridge  under 
the  shoe  and  conduct  a  bailing  test.  It  often  happens  that  a  bridge  does 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  29 

not  form  a  water-tight  bond  with  the  walls  of  the  hole,  in  which  case 
water  may  come  from'  below.  If  the  bridge  is  tight,  water  may  come 
from  defective  casing,  defective  shut-off,  or  from  any  porous  formation 
existing  between  the  top  of  the  bridge  and  the  shoe  of  the  water  string. 
The  general  conditions  governing  such  a  test -are  outlined  in  the  previous 
discussion  of  original  tests  of  shut-off  (pp.  19-21). 

(b) — If  water  is  found  to  be  entering  the  well  above  the  bridge,  re- 
test  the  casing  for  leaks. 

(c) — If  test  (a)  shows  that  the  well  still  makes  water,  or  does  not 
account  for  all  of  the  water  that  was  being  produced,  the  bottom  of  the 
well  may  be  plugged  with  cement  for  a  certain  distance.  After  the 
cement  has  set,  a  bailing  test  should  be  made.  If  the  well  still  makes 
water,  continue  plugging  and  testing  in  stages  until  the  source  of  the 
water  is  determined  and  the  water  is  shut  off. 

(7) — Use   of   Dye   or  Colorless   Substance  for  Tracinq   Underground    Flow  of 
Water: 

Suitable  dyes  can  sometimes  be  used  to  good  advantage  for  indicating 
underground  fluid  connections  and  the  direction  of  movement.  Dye  can 
also  be  used  for  testing  the  efficiency  of  a  water  string. 

The  World  War  has  greatly  retarded  the  use  of  dyes  since  1914,  duo 
to  scarcity  and  prohibitive  prices.  Varying  degrees  of  success  have  ac- 
companied experiments  in  connection  with  oil  field  conditions.  Some  dyes 
are  decolorized  by  the  reducing  action  of  petroleum  compounds  and  by 
hydrogen  sulphide,  or  are  absorbed  by  mud  and  formations.  Such  dyes 
are  usualy  unsuitable  for  oil  well  purposes. 

The  subject  has  not  received  the  attention  it  merits,  and  it  is  be- 
lieved that  experimental  work  would  point  to  a  means  of  using  dyes  more 
advantageously  in  tracing  water.  Some  of  the  dyes  that  are  absorbed 
or  reduced  by  crude  oil  may  be  used  successfully  when  the  fluid  carries  a 
large  percentage  of  water. 

It  is  said  that  the  dye  eosin  is  not  affected  by  hydrogen  sulphide, 
nitric  acid,  magnesium  sulphate,  sodium  hydroxide,  alcohol  or  gasoline. 
The  price  and  supply,  however,  prohibit  its  use  at  present. 

The  United  States  Geological  Survey  has  used  fluorescein  for  tracing 
the  flow  of  underground  waters  in  connection  with  water  supply  problems. 
It  is  said  to  be  a  delicate  dye  which  is  only  slightly  affected  by  the  nor- 
mal ingredients  of  natural  waters;  to  be  decolorized  by  acids  and  affe-cted 
by  some  forms  of  unstable  organic  matter.  A  loss  of  color  due  to  acidity 
can  be  restored  by  making  the  sample  alkaline.  Stabler*  points  out  that 
fluorescein  can  be  noted  with  the  eye  in  solutions  as  weak  as  one  part 
in  40,000,000  parts  of  water  and  that  one  part  in  10.000,000,000  can  be  de- 
tected with  the  aid  of  a  long  glass  tube.  He  considers  it  the  most  effi- 
cient dye  for  tracing  underground  flowrs  of  water.  In  a  personal  inter- 
view, Mr.  Stabler  stated  that  this  dye  can  be  obtained  from  the  Eastman 
Kodak  Company,  Rochester,  N.  Y.,  at  a  price  of  about  $10.00  per  pound 
and  that,  regardless  of  its  price,  it  is  probably  the  most  desirable  dye 
to  use. 

The  chemical  nature  and  intensity  of  a  dye  will  influence  the  amount 
that  should  be  used  for  a  given  set  of  conditions.  In  testing  the  elTiciency 
of  a  water  string,  two  to  five  pounds  of  good  dye  would  probably  suffice, 
while  for  use  to  show  underground  flow,  ten  pounds  or  more  wou!d  be 
advisable.  When  testing  a  water  string,  the  dye  is  put  behind  such  casing 
and  washed  down  with  a  stream  of  water.  The  pumping  of  the  well 
should  not  be  suspended.  The  appearance  of  dye  in  the  production  will 
indicate  a  casing  leak  or  defective  shut-off.  When  testing  for  under- 
ground connection,  the  dye  should  be  released  at  the  bottom  of  the  sus- 
pected well  and  this  well  should  remain  shut  down  during  the  time  of 
test.  It  is  important  to  remember  that  dye  placed  in  the  bottom  of  well 
No.  1  and  showing  in  well  No.  2  is  not  conclusive  proof  that  well  No.  1 
i^  at  fault.  The  current  of  water,  flowing  in  the  general  direction  No.  1- 
No.  2,  may  be  due  to  imperfections  in  one  or  more  other  wells. 


~*S  fabler.  Herman  (Chief  Engineer.  Land  Classification  Board.  [\  S.  Geo- 
logical Surrey),  Engineering  Investigations.  The  Reclamation  Record  (Depart- 
ment of  the  Interior)  J'ol.  '/*,  Xo.  .?.  March.  19?!. 


30  EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 

It  is  stated  by  A.  W.  Ambrose,  chief  petroleum  technologist  of  the 
Bureau  of  Mines,  that  "acid  orange"  is  a  cheap  and  reliable  dye  for 
average  sub-surface  conditions.  The  cost  or  this  dye  is  about  90  cents 
per  pound  and  is  obtained  from  Hemingway  &  Company,  New  York.  A 
Prussian  blue  is  reported  to  have  been  successfully  used  in  a  number  of 
cases,  and  it  seems  to  meet  the  general  requirements  of  oil  field  condi- 
tions. It  is  a  cyanide  of  iron,  and  the  writers  are  not  fully  advised  as 
to  the  effect  that  sulphur  compounds  may  have  upon  it.  It  is,  however, 
probably  one  of  the  most  reliable  and  available  dyes  for  present  use. 

It  is  understood  that  the  underground  flow  of  water  has  been  traced 
by  colorless  substances  which  the  water  did  not  originally  contain  except 
in  comparatively  small  quantities.  For  instance,  one  of  the  rare  elements, 
such  as  lithium,  may  be  added  in  small  quantity  and  samples  from  some 
other  point  tested  by  spectroscopic  analyses.  Or  an  excess  of  .a  com- 
pound, such  as  chlorides  or  sulphates,  may  be  added  and  the  samples 
tested  by  measuring  the  resistance  to  an  electric  current,  or  by  chemical 
means. 

(8) — Packers   Used   in   Casing  or  in   Formation: 

Packers  run  into  the  wells  on  tubing  or  casing  and  set  in  casing  or 
formation  are  used  to  good  advantage  for  testing  the  source  of  the  water. 
The  packer  is  supposed  to  form  a  tight  bond  between  the  wall  of  the 
hole  or  the  inside  of  the  casing  and  the  tubing  or  casing  on  which  it  is 
set  and  thus  retards  the  fluid  moving  past  the  point  at  which  the  packer 
is  set.  The  subsequent  testing  by  bailing  or  pumping  is  done  below  the 
packer,  whereas  in  the  case  of  a  bridge,  the  reverse  is  true. 

A  packer  is  usually  employed  for  testing  and  Avith  the  idea  that  if  it 
excludes  the  water,  it  will  remain  in  the  hole.  The  common  packer  makes 
use  of  an  expanding  rubber  or  canvas  to  effect  a  seal.  Although  the  rub- 
ber is  decomposed  in  time  by  oil  and  water,  such  packers  have  frequently 
been  left  in  wells  of  other  fields  for  permanent  correction  of  water  trou- 
bles. Hemp  has  been  used  successfully  in  this  connection,  and  will  prob- 
ably last  longer  than  rubber.  The  efficiency  of  a  packer  may  sometimes 
be  increased  by  caving  formation  or  by  the  addition  of  mud  or  sand  put 
in  from  the  surface.  Experience  has  shown  in  some  fields  that  packers 
should  not  be  used  against  the  formation,  if  a  permanent  water  shut-off 
is  to  be  expected. 

(9) — Use  of   Muddy   Water  to    Indicate    Point  of   Entry: 

The  point  of  entry  of  water  into  a  well  may  sometimes  be  determined 
by  using  thin  mud  fluid  or  muddy  water.  The  well  should  be  filled  as 
high  as  practicable  with  muddy  water,  with  the  hole  open  to  bottom  or 
otherwise.  The  fluid  should  then  be  bailed  off  the  top  and  a  careful  watch 
kept  to  note  the  thinning  of  the  mud  and  the  appearance  of  clear  water. 
As  the  fluid  level  is  lowered  in  the  hole,  the  head  of  infiltrating  water  will 
again  over-balance  the  fluid  column  in  the  well,  with  the  result  of  thin- 
ning up  the  mud  with  clear  water.  As  soon  as  the  bailer  has  reached  the 
point  of  inflow,  it  will  pick  up  practically  clear  water.  The  point  of  in- 
flow is  thereby  approximately  located. 

(10) — Relation   of   Sequence   of   Wells   "Going   to   Water"   to   Geologic   Struc- 
ture: 

Water  which  occurs  in  the  down-dip  portion  of  an  oil-bearing  stratum 
is  called  "edge-water."  As  the  oil  is  removed  by  producing  wells,  the 
water  will  replace  it.  The  head  of  the  encroaching  water  will  be  a  lac- 
tor  in  its  rate  of  progress,  as  will  the  off-setting  oil  and  gas  pressure.  In 
strata  of  low  inclination,  such  as  at  El  Dorado,  the  line  of  encroachment 
will  be  quite  irregular  and  will  be  controlled  largely  by  the  poresity  and 
texture  of  the  edge-water  sand. 

The  classification  of  a  water  as  edge-water  would  usually  be  based 
solely  upon  the  evidence,  of  down-dip  wells  going  to  water  first.  The 
available  means  of  determining  the  stratum  through  which  encroachment 
is  taking  place  are  not  usually  different  from  those  described  'elsewhere 
for  locating  the  point  of  entry  of  water  into  a  well.  It  may  occasionally 
happen  that  a  clue  is  readily  available  owing  to  the  fact  that  rrome  of  the 
down-dip  wells  are  not  as  deep  stratigraphically  as  the  others.  This  con- 
dition would  probably  eliminate,  some  of  the  strata  as  edge-water-bearing 
possibilities. 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 


(11) — Comparison   of   Chemical    Analyses   of  Waters: 

It  has  been  demonstrated  that  a  careful  investigation  of  numerous 
chemical  analyses  will  usually  disclose  identical  characteristics  of  the 
waters  of  each  horizon;  and  that  these  characteristics  are  apt  to  persist 
in  general  over  the  area  of  an  oil  field.  It  is  reasonable  to  assume  that, 
if  the  waters  of  different  depths  are  restrained  from  mixing,  differem 
conditions  will  obtain  and  render  them  dissimilar.  Some  of  the  controlling 
factors  affecting  the  mineral  contents  of  the  water  are  temperature,  pres- 
sure, time  of  contact  with  formation,  distance  traveled  through  forma- 
tions, chemical  nature  of  the  reservoir  formations,  quantity  of  water,  ana 
the  accessibility  of  meteoric  water  to  the  point  of  sampling.  The  best 
results  from  water  analyses  can  be  expected  where  the  structural  move- 
ments have  not  permanently  destroyed  the  impervious  character  of  inter- 
zonal formations.  The  intermingling  of  waters  along  fault  planes  and 
through  crushed  zones  will,  of  course,  minimize  the  possibility  of  a  defi- 
nite conclusion  from  analyses. 

Chemical  analyses  have  been  used  in  several  fields  to  determine  the 
source  of  the  water  produced  by  oil  wells.  This  work  has  shown  that  the 
engineer  can  not  use  analyses  of  one  field  as  an  indication  of  the  chem- 
ical properties  of  the  water  of  another  field.  Any  attempt  to  use  chemical 
analyses  of  waters  at  El  Dorado  must  be  carried  on  as  an  investigation 
entirely  independent  of  the  findings  in  other  fields.  Samples  of  water 
from  definite,  known  sands  should  be  analyzed  and  then  later  when  a  well 
makes  water  whose  source  is  unknown,  a  sample  can  be  collected  for 
analysis.  The  analysis  of  this  water  can  then  be  compared  with  the 
known  samples,  so  as  to  determine  the  origin  of  the  water. 

Analyes  of   Underground   Waters  of  the   El    Dorado   Field: 

Table  No.  4  gives  the  results  of  analyses  of  four  samples  of  water 
from  El  Dorado  wells  (probably  edge  or  so-called  bottom  water)  and  of 
two  samples  of  known  top  water  from  shallow  water  wells.  The  analyses 
were  made  by  W.  F.  Fulton  of  the  Louisiana  Oil  &  Refining  Company  at 
Shreveport,  Louisiana,  and  by  W.  B.  Lerch  of  the  U.  S.  Bureau  of  Mines 
at  Bartlesville,  Oklahoma. 

Lack  of  time .  prevented  a  complete  collection  of  water  and  compila- 
tion of  their  analyses.  The  few  samples  examined  showed  a  very  marked 
difference  in  the  chemical  properties  of  upper  and  lower  waters.  The  gen- 
eral differences  adhere  rather  closely  to  the  differences  in  waters  of  some 
other  fields  as  pointed  out  by  Rogers*  The  difference  in  total  solids  is 
the  most  notable  and  it  has  an  important  influence  on  the  percentage 
figures  shown  in  Table  No.  4.  For  instance,  the  first  analysis  shows  48.52 
per  cent  chlorine  and  the  last  shows  40.01  per  cent.  There  is,  however, 
about  628  times  more  chlorine  in  the  first  sample  (bottom  water)  than  in 
the  last  (top  water).  The  samples  of  top  water  were  taken  from  com- 
paratively shallow  depths  and  the  character  of  any  deeper  top  water  is. 
therefore,  uncertain.  Because  all  wells  have  been  drilled  with  rotary 
tools,  it  has  been  impossible  to  obtain  any  samples  of  lower  top  waters. 
The  bottom  or  edge  water  at  El  Dorado  has  a  distinctly  salty  taste.  The 
facr  that  the  large  producers  of  water  also  make  water  with  a  similar 
taste  indicates  that  the  large  water  producers  are  making  edge  or  bot- 
tom water.  As  remedial  work  is  undertaken,  chemical  analysis  may  be 
found  useful. 

(12) — Accompanying   Oil   and   Emulsion: 

When  water  and  oil  are  intimately  mixed  by 'agitation,  an  emulsion  is 
formed.  It  is  known  to  be  formed  by  such  conditions  as  the  sudden  ex- 
pansion of  gas  in  the  presence  of  oil  and  water  and  by  the  passage  of 
oil  and  water  through  small  openings,  such  as  leak-back  past  a  worn  "bnl?. 
and  seat  of  a  pump,  between  tight-fitting  liner  or  screen  and  oil  string., 
past  defective  bottom  plug  and.  through  the  oil-bearing  formations.  It  ap- 
pears likely  that  emulsion  may  be  formed  at  the  surface  as  well  as  un- 
derground. 


*Rt>f/e>'s,  G.  S.,  Chemical  Relations  of  the   OH  Field  ]\'atcrs  in   San  Joaquin 
l-'nllev,  Calif nrnin.  II.  S.  G.  S.  Bull.  6si.  IQI?.  ' 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


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EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 33 

Association   of  Oil   and   Water: 

A  correct  idea  of  the  underground  relation  existing  between  the  oil 
and  water  appearing  in  production,  is  essential  to  establish  the  best  prac- 
tice for  the  removal  of  the  maximum  amount  of  oil  and  gas.  In  studying: 
this  phase  of  the  subject,  the  evidence  was  found  to  be  rather  meager  on; 
account  of  poor  logging  or  slight  distance  drilled  into  the  oil  sand. 

Plate  VII  was  constructed  from  thirty-eight  well  logs  for  the  purpose 
of  estimating  the  character  of  the  oil  and  water  zones.  Plate  IV  was  pre- 
sented to  generalize  the  conclusions  drawn  from  information  at  hand. 

The  north-south  generalized  section  of  Plate  IV  represents  conditions- 
along  the  high  portions  of  the  structure  and  also  the  variance  in  certain 
features  from  north  to  south.  The  convolutions  of  the  strata  represent 
saddles  along  the  axes  of  the  structure.  It  is  assumed  that  the  oil  zone 
proper  is  free  from  edge  water  along  the  higher  portion.  The  dip  is  ex- 
aggerated fifty  times  in  both  sections,  the  horizontal  scale  being  1,000  feet 
to  the  inch  and  the  vertical  scale  being  twenty  feet  to  the  inch.  These 
scales  are  used  for  proportioning  the  thickness  of  sand  and  its  change  in 
elevation,  but  the  remaining  features  are  necessarily  generalized. 

The  fault  shown  in  Plate  IV  is  assumed  for  the  reason  that  it  makes 
a  rather  sudden  change  from  productive  to  practically  non-productive  ter- 
ritory, and  from  light  oil  to  heavy  oil. 

The  oil  sand  proper  varies  in  texture  from  sand  to  sandy  shale  and  in 
thickness  from  about  sixteen  feet  at  the  north  end  to  about  ten  feet  at 
the  south  end.  The  sand  is  less  prolific  in  some  parts  of  the  field  than 
in  others.  The  logs  show  that  a  hard  cap  rock,  one  to  two  feet  in  thick- 
ness, is  encountered  uniformly  just  above  the  oil  sand  in  the  north  end 
of  the  field.  South  of  about  the  middle  of  Section  8-18-15.  such  a  cap  rock 
is  not  generally  logged.  It  appears  likely  that  a  hard  rock  layer  does  not 
overlie  the  oil  sand  in  the  southern  portion  of  the  field  and  that  some  of 
the  wells,  logging  a  cap  rock,  have  encountered  the  lower  cap  rock  in- 
stead. A  cap  rock  below  the  oil  sand  proper  appears  to  persist  through- 
out the  field.  Below  this  cap  is  a  zone  of  variable  texture  that  appears  to 
carry  both  oil  and  water.  Deposits  of  oil  have  been  retained  under  the 
highest  portions  of  the  persistent  second  cap  rock  and  in  places  appar- 
ently under  local  impervious  partings. 

Below  the  second  zone,  which  is  about  twenty  feet  thick,  a  third  cap 
rock  was  logged  in  a  number  of  wells,  under  which  occurs  another  sandy 
zone  that  carries  salt  water.  The  sands  between  the  first  and  third  cap* 
rocks  are  usually  designated  in  the  well  logs  as  the  oil  sand. 

Wells  that  are  drilled  just  into  the  sand,  below  the  second  cap  roclc 
on  high  points  of  the  structure,  may  make  clean  oil  if  they  are  suffi- 
ciently controlled  (i.  e.,  their  flow  restricted)  to  avoid  water  coning. 
Wells  located  far  down  on  the  structure  within  range  of  edge  water, 
should  also  produce  clean  oil  if  drilled  only  a  few  feet  into  the  main  oil 
sand  and  restricted  so  that  they  will  not  produce  too  fast  from  the  bot- 
tom of  the  sand.  The  east-west  section  of  Plate  IV  illustrates  the  un- 
derground conditions  to  be  dealt  with. 

Some  operators  believe  that  the  lifting  of  excessive  water  must  be 
taken  as  a  matter  of  course  in  cases  of  this  kind.  In  the  higher  por- 
tions of  the  structure,  there  was  probably  little  or  no  water  originally 
in  the  first  oil  zone.  As  the  pressure  was  reduced  and  oil  removed,  edge 
water  encroached  further  up  the  dip.  Moreover,  when  wells  are  drilled 
far  enough  down  slope,  edge  water  may  easily  be  drawn  into  them  from 
the  bottom  of  the  sand,  if  they  are  pumped  hard  or  allowed  to  flow  full 
capacity,  even  though  they  have  barely  penetrated  the  oil  sand. 

In  this  field,  when  the  top  of  the  oil  sand  lies  as  low  as  1,935  feet 
below  sea  level,  the  sand  should  be  barely  touched  when  drilling  in  and 
the  output  restrained  considerably  below  the  full  capacity  of  the  well. 
This  should  not  be  interpreted  to  mean  that  wells  in  which  the  oil  sand 
was  found  at  shallow  depths  below  sea  level,  such  as  1,930  or  1,925  feet, 
can  be  drilled  deep  into  the  sand  and  "pulled  hard,"  without  danger 
of  drawing  in  edge  water.  All  high-pressure  wells  must  be  controlled  in 
this  field,  not  only  to  avoid  the  "drawing  in"  of  edge  water,  but  to  pre- 
vent them  from  drilling  themselves  deeper  into  the  soft  and  consoli- 
dated sand  body. 


34 EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 

Thus  the  evidence  indicates  that  clean  production  can  be  expected 
from  wells  that  are  fairly  high  on  the  structure,  that  are  drilled  only  a 
few  feet  below  the  top  of  the  oil  sand  and  that  are  kept  under  proper 
control.  Exceptions  to  this  rule  would  be  due  to  the  letting  in  of  water 
by  neighboring  wells  or  the  production  of  top  water. 

The  wells  shown  in  Plate  IV  are  hypothetical  wells,  drawn  to  repre- 
sent the  following  conditions  which  exist  in  various  parts  of  El  Dorado 
field: 

Wells  A  and  I:  Low  on  the  flanks  of  the  structure.  Drilled  too  deep 
or  produced  too  rapidly,  resulting  in  the  drawing  in  of  edge  water. 

Wells  B  and  G:  Bottom  of  hole  rather  close  to  edge  water  level  in 
the  sand,  but  can  produce  large  quantities  of  clean  oil  by  "pinching 
down." 

Wells  C,  M  and  S:  Drilled  too  -deep  and  penetrated  second  sand  at 
points  where  it  carries  water.  These  wells  are  flooding  the  upper  produc- 
tive sand  with  water. 

Wells  D,  F,  N  and  R:  Drilled  to  proper  depth  and  cased  properly,  but 
making  water  let  into  the  sand  by  other  wells. 

Well  E:  Drilled  through  third  cap  into  bottom  water,  plugged  back 
but  not  high  enough  to  catch  second  cap,  flooding  oil  sand  with  water. 

Well  H:  Low  on  structure  and  originally  made  edge  water.  Plugged 
part  way  back  to  cut  off  entrance  of  water.  This  well  should  make  con- 
siderable oil  if  properly  controlled. 

Well  J:  East  of  probable  fault,  oil  low  gravity  and  a  great  deal  of 
water,  entered  deposits  of  heavy  oil,  non-commercial  at  present. 

Wells  K,  P  and  T:  High  on  structure,  producing  clean  oil  and  no 
water. 

Wells  L  and  U:  Drilled  through  second  cap  rock,  but  properly  plugged 
to  exclude  water. 

Wells  O  and  V:  Drilled  just  below  second  cap  into  underlying  oil  on 
structural  highs,  produced  too  rapidly,  causing  water  coning. 

Well  Q:     Drilled  into  bottom  water  and  not  plugged,  flooding  oil  sand. 

In  the  case  of  Well'N,  it  will  pay  to  plug  with  cement  to  a  point  sev- 
eral feet  above  the  contact  between  the  water  and  oil,  providing  the  sand 
is  reasonably  consolidated.  If  water  with  a  high  head  has  access  to  a 
hole,  the  water  will  soon  prevent  the  entry  of  oil  into  the  hole.  Where 
there  is  no  parting  between  the  water1  and  oil,  a  plug  cannot  be  expected 
to  hold  the  water  back  indefinitely.  However,  the  water  cannot  enter  the 
hole  as  freely  as  in  the  case  of  open  hole,  because  it  must  pass  upward 
through  a  greater  thickness  of  formation,  with  a  resulting  increased  re- 
sistance from  the  formation.  In  doing  so,  some  of  the  oil  is  pushed  ahead 
of  the  water,  also  the  oil  has  a  longer  period  lor  draining  laterally  into  the 
hole  which  often  results  in  an  increased  extraction  of  oil. 

An  example  of  the  harmful  effect  that  an  improperly  drilled  well  can 
have  on  a  correctly  drilled  well,  is  here  given.  In  El  Dorado,  Well  A  was 
drilled  too  deep  with  rotary  and  produced  a  large  amount  of  salt  water 
with  the  oil.  Well  B,  about  300  feet  away,  was  carefully  finished  about 
one  foot  below  the  top  of  the  oil  sand  with  cable  tools  shortly  after  A 
came  in.  Well  A  had  been  flowing  an  oil-water  fluid  vigorously  and  B  also 
flowed  oil  for  a  short  time.  Muddy  salt  water  then  appeared  in  B,  which 
was  strong  evidence  that  rotary  mud  and  water  had  entered  from  A,  as 
these  two  wells  were  practically  isolated  at  that  time.  The  flow  in  B 
quickly  subsided  and  it  was  then  pumped.  The  oil  production  was,  com- 
paratively small  and  the  water  continued  to  appear  in  large  quantities. 
Neither  Well  A  nor  B  will  show  a  profit  unless  A  is  repaired  properly  and 
promptly. 


Use  of  Cement 


In  the  history  of  the  oil  industry,  many  methods  have  been  devised 
for  the  exclusion  of  water.  For  shutting  off  top  water  with  casing,  the  for- 
mation shut-off,  seed  bag  or  other  material  that  will  swell  behind  the  pipe, 
tamping  method,  various  types  of  packers,  mud-fluid  in  combination  with 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 35 

formation  shut-oft's,  and  cement  have  been  used.  For  bottom  water,  the 
tamping  of  various  substances,  mechanical  plugs  and  cement  (sometimes 
in  combination  with  mud)  have  been  used.  Of  these  several  methods  of 
excluding  water,  in  many  cases,  cement  has  proved  to  be  highly  satisfac- 
tory for  both  classes  of  work.  Mud  fluid  is  in  many  fields  of  considerable 
use,  particularly  in  top  water  shut-offs.  It  is  not  serviceable  when  used 
alone  for  high-pressure  bottom  water.  It  is  often  necessary  to  use  me- 
chanical devices  or  mud-fluid  in  connection  with  cement  for  the  purpose  of 
clogging  porous  formations  and  stopping  the  movement  of  water,  oil  or 
gas. 

The  use  of  cement  behind  water  strings  has  been  quite  diverse  in  ap- 
plication. Detailed  descriptions  of  cementing  methods  have  been  de- 
scribed by  Tough.* 

A  brief  description  of  the  various  ways  of  cementing  in  different  fields 
is  here  given.  Cement  has  been  placed  behind  casing  (1)  by  dumping  it 
outside  of  the  casing  at  the  surface;  (2)  by  lowering  the  casing  into  the 
mixed  cement  which  has  been  placed  at  the  bottom  of  the  hole  and  effect- 
ing no  change  in  the  height  of  the  cement  inside  and  outside  the  casing; 
(3)  by  placing  the  cement  in  the  bottom  of  the  hole  by  pouring  it  in  dry 
or  mixed,  or  with  a  dart  bailer  (adapted)  or  dump  bailer  and  then  lower- 
ing the  casing  into  the  cement  with  a  plug  in  the  bottom  of  the  casing  or 
with  a  head  on  top,  having  the  casing  full  of  water,  thus  leaving  little  or 
no  cement  in  the  shoe  joint;  (4)  by  pumping  the  cement  through  tubing, 
with  or  without  the  aid  of  one  or  two  wooden  plugs  to  determine  the 
travel  of  the  cement,  following  with  water  or  mud,  and  using  a  packer  at 
bottom  or  a  packing  head  at  top;  (5)  by  pumping  cement  through  the 
casing  and  following  it  with  water  or  mud,  using  no  plugs  to  determine  the 
travel  of  the  cement  and  to  prevent  its  mixing  with  other  fluids;  (6)  by 
the  same  method  as  number  5,  except  using  one  plug  after  the  cement;  (7) 
by  the  same  method  as  number  5,  except  using  one  plug  before  and  one 
plug  after  the  cement. 

Method  1  is  unreliable  and  has  not  been  attempted  to  any  extent.  In- 
deed, the  conditions  allowing  its  use  are  not  frequently  met.  Method  2  is 
not  reliable,  especially  for  rotary  holes,  because  there  is  little  or  no  -clean- 
ing action  on  the  walls  by  the  cement.  The  more  cement  that  is  used,  the 
more  it  is  necessary  to  drill  out.  In  method  3,  good  work  has  been  done 
with  the  dump  bailer,  using  small  amounts  of  cement,  but  it  is  not  suitable 
for  rotary  holes,  unless  the  formation  will  stand  washing,  on  account  of 
probable  inability  to  properly  free  the  walls  of  mud  with  a  large  amount 
of  cement.  Method  4  has  been  used  to  good  advantage,  especially  when  a 
small  quantity  of  cement  or  a  quick-setting  cement  is  used.  The  cement 
can  be  put  away  in  quicker  time  with  tubing  than  with  casing.  The 
method,  however,  is  now  practically  obsolete  for  casing  jobs.  Method  5, 
although  used  in  some  fields,  is  not  considered  reliable,  as  there  is  danger 
of  diluting  the  cement  or  of  leaving  too  much  cement  in  the  casing.  By 
method  6,  it  becomes  known  when  the  cement  is  all  out  of  the  casing,  but 
unless  a  large  quantity  of  cement  is  used,  the  excessive  dilution  of  the 
first  of  the  cement  column  may  render  the  work  unsuccessful.  Method  7 
is  considered  the  most  reliable  cementing  practice  that  has  been  developed. 
There  are  various  modifications  of  this  practice,  but  in  principle  the  first 
plug  prevents  the  dilution  of  the  cement  with  the  fluid  in  the  pipe  and 
allows  its  passage  after  that  plug  reaches  bottom,  while  the  second  plug 
protects  the  upper  part  of  the  cement  column  and  indicates  when  the 
cement  is  all  out  of  the  casing,  by  stopping  or  slowing  the  pump.  The 
first  plug  remains  in  the  bottom  of  the  casing  and  the  last  plug  cannot 
leave  the  casing.  The  most  efficient  plugs  are  made  of  wood  with  circu- 
lar pieaes  of  belting  to  fill  out  the  full  diameter  of  the  pipe,  except  that 
an  inverted  leather  cup  should  be  placed  on  top  of  the  second  plug. 

Probably  the  most  improved  practice  in  connection  with  the  two-plug 
system  of  cementing  water  strings  is  found  in  the  patented  Halliburton 
and  Perkins  methods.  In  the  former,  the  exact  position  of  the  last  plug, 
which  follows  the  cement,  is  always  known  by  reading  a  steel  tape.  The 


*Tough,  F.  B.,  Methods  of  Shutting  off  Water  in  Oil  and  Gas  Wells,  Bul- 
letin 163,  U.  S.  Bureau  of  Mines,  1918. 


36 EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

tape  is  attached  to  the  plug,  runs  through  a  packing  device  and  is  fed  from 
a  reel  and  over  a  pulley.  This  apparatus  is  coming  into  extensive  use  in 
various  fields  of  the  country,  particularly  in  southern  Oklahoma.  A  full 
description  is  given  by  Swigart  and  Schwarzenbek.*  The  position  of  the 
plugs  is  checked  by  reading  a  water  meeter. 

At  El  Dorado  the  general  practice  has  been  to  use  only  one  wooden 
plug  with  a  sack  of  shale  placed  on  top  of  it,  to  follow  the  cement.  The 
sack  of  shale  is  meant  to  act  in  the  same  manner  as  an  inverted  cup,  i.  e., 
stall  the  pump  when  the  plug  reached  bottom.  This  practice,  although  ap- 
parently successful,  is  not  always  as  reliable  as  the  two-plug  method. 

The  use  of  a  loosely-filled  sack  of  fine  shale  following  a  plain  wooden 
plug,  is  no  doubt  an  efficient  method  of  stopping  the  pump  at  the  end 
point,  provided  the  shale  is  retained  in  the  sack.  The  sack  may  become 
torn  before  it  travels  very  far  and  the  particles  of  shale  separated  from 
the  top  of  the  plug.  If  this  happens,  circulation  may  obtain  between  the 
plug  and  the  casing,  when  the  plug  reaches  bottom,  and  thus  carry  the 
cement  up  above  the  casing  shoe.  As  a  matter  of  fact,  if  the  plug  is 
almost  the  same  diameter  as  that  of  the  casing,  the  pumps  will  be  slowed 
up  so  appreciably  when  the  plug  reaches  bottom,  that  it  would  be  dis- 
tinctly noticeable. 

Because  of  the  large  amount  of  bottom  hole  plugging  which  will  even- 
tually have  to  be  done  in  El  Dorado  oil  field,  a  brief  discussion  of  plugging 
with  cemeut  will  be  included.  Cement  for  bottom  water  jobs  in  other 
fields  has  been  handled  in  different  ways;  (1)  by  pouring  dry  or  mixed 
cement  into  the  casing  at  the  surface;  (2)  by  placing  mixed  cement  on  the 
bottom  with  a  dart  or  dump  bailer;  (3)  by  dropping  cement-filled  metal 
containers  to  bottom  and  breaking  these  up  with  the  tools;  (4)  by  pump- 
ing cement  through  tubing  and  holding  a  pressure.  Method  1  is  almost 
certain  of  failure.  With  Method  2,  small  quantities  of  cement  can  be  suc- 
cessfully placed  on  bottom  with  a  dart  bailer  and  more  can  be  added  if 
some  device  is  used  to  hold  the  dart  open  after  it  trips.  The  use 
of  a  dump  rod  attachment  injures  the  cement.  The  dump  bailer  is  a 
thoroughly  reliable  tool  for  such  work  and  should  always  be  used  in  pref- 
erence 'to  other  bailers.  Fig.  2  shows  one  of  the  common  types  of  dump 
bailer.  This  device  can  be  used  very  successfully  when  the  walls  of  the 
hole  to  be  cemented  are  fairly  clean,  when  all  gas,  oil  or  water  movement 
has  been  stopped  and  when  it  is  not  necessary  to  force  cement  into  the 
pores  of  the  formation.  Method  3  has  been  used  quite  successfully  in  dif- 
ferent fields.  It  offers  opportunity  for  quieting  very  weak  fluid  movement 
by  the  tamping  effect  and  thus  allowing  the  cement  to  set  on  top  of  the 
tamp.  It  is  a  convenient  method  to  try  where  apparatus  for  better 
methods  is  lacking. 

Method  4  is  a  very  satisfactory  way  to  cement  off  bottom  water  with 
a  high  head.  As  shown,  C  of  Plate  III,  the  tubing  is  run  nearly  to  bot- 
tom of  the  hole  through  a  casinghead  packer,  which  has  an  outlet  valve. 
The  tubing  should  first  be  run  to  bottom  and  circulation  of  mud  started  to 
clean  out  collected  debris.  After  circulation  is  gained,  the  cement  is  then 
started  through  the  pump  with  or  without  preceding  it  with  a  wooden  plug. 
When  a  plug  is  not  used,  the  cubic  contents  of  the  tubing  are  calculated. 
The  progress  of  the  cement  can  be  checked  by  a  water  meter.  In  this 
method  it  is  important  to  know  when  the  first  cement  reaches  bottom  and 
it  becomes  impracticable  to  measure  mixed  cement  from  a  tank. 

If  a  plug  is  used,  the  pump  will  be  checked  when  the  first  cement 
reaches  bottom,  because  the  tubing  is  not  held  high  enough  to  allow  the 
plug  to  pass  entirely  out.  In  any  event,  when  the  cement  reaches  bot- 
tom, the  tubing  should  be  raised  slightly  above  the  renuired  depth  for  the 
top  of  the  cement  plug,  and  the  outlet  valve  on  the  casing  should  be  closed. 
The  cement  is  then  forced  against  the  walls  of  the  hole  and  into  the  pores 
of  the  formation.  If  the  cement  is  readily  absorbed  by  the  formations,  it 


*Swigart.  T.  E.,  and  Schwarzenbek.  F.  X.,  Petroleum  Engineering  in  the 
Hewitt  Oil  Field,  Oklahoma — Co-operatirc  Report  of  State  of  Oklahoma  and 
U.  S.  Bureau  of  Mines,  January,  1921.  Distributed  by  Ardmorc  Chamber  o\ 
Commerce.  Price,  $1.00. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


37 


SPECIFICATIONS  AND  USE 

1  -  Make  reins  of  ifinch  square  iron  as  far  as  6 -inches  below 

the  latch  and  f-inch  square  iron  below  that  point,  allowing 
a  larger  space  for  filling  with  cement. 

2  -Chains  should  be  finch  Swedish  steel  for  6|-inch,  or  small- 

er, and  f-inch  material  for  larger  than  6|-inch  bailer. 

3  -Chains  should  be  fastened  to  removable  eye-bolt  which  ex- 

tends  through  the  valve,  facilitating  repairs  and  transpor- 
tation. 

4  -Use  only  neat  cement  and  fresh  water,  i.e.  cement  without 

sand,  rock  or  other  material. 

5  -  Proper  mix  about  45  pounds  water  to  100  pounds  cement. 

6  -Mix  thoroughly  and  rapidly. 

7  -Just  sufficient  cement  to  fill  bailer  should  be  mixed  at  once. 

8  -  When  lowering  cement-filled  bailer,  run  slowly  enough  to 

avoid  latch  moving  below  bail  and  dumping  cement  above 
bottom  when  slow  motion  is  resumed. 

9  -Care  should  be  taken  not  to  trip  the  latch  when  bailer  hits 

top  of  water. 

10- A  sectional  bailer; made  of  several  joints  of  pipe,  should  be 
used  when  it  is  desired  to  dump  a  considerable  quantity  of 


1 1  —  Before  cementing,  stop  gas  or  water  movement  at  cement- 
ing point  with  a  sufficient  head  of  water,  or  with  mud. 

12 -Avoid  dilution  of  cement,  after  opening  valve,  by  holding 
bottom  of  bailer  at  top  of  loose  cement  a  sufficient  time 
to  finish  emptying  cement  from  bailer. 

13 -Cement  should  be  allowed  10  days  to  set.  Maintain  a  con- 
stant head  of  water  during  that  time. 


a 


U.  S.  BUREAU  OF  MINES 

PETROLEUM  DIVISION 
DAI!AS,  TEXAS. 


SKETCH  SHOWING 

DUMP  BAILER  FOR 

CEMENTING  OIL  WELLS 


Drawn  by  J.  G.  Shumate  Dare  flr      11.  1921 
Scale,  Diggrammau  


Fig.   II.      Dump   Bailer,  p.  102. 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


is  necessary  to  have  enough  in  readiness  to  supply  the  needs  of  a  predeter- 
mined pressure  or  to  know  when  the  last  cement  has  left  the  tubing.  This 
can  be  ascertained  accurately  by  a  wooden  plug  following  the  cement  or 
by  reading  a  water  meter,  through  which  passes  the  water  pumped  into 
the  well.  When  the  cement  is  all  out  of  the  tubing,  the  tubing  is  raised  off 
the  plug,  and  the  pumping  is  resumed  with  the  outlet  valve  at  the  casing- 
head  partly  open.  Any  cement  that  may  have  risen  above  the  desired  point 
can  be  circulated  out.  Care  must  be  taken  to  maintain  a  constant  pressure 
or  otherwise  the  cement  may  not  remain  at  rest  and  thereby  fail  to  set. 

In  using  the  above  method,  it  is  obvious  that  the  cement  introduced  and 
followed  by  the  second  plug,  may  not  be  enough  to  fill  up  the  cavity  and 
pore  spaces  under  the  desired  pressure.  In  that  event,  more  cement  can 
be  added,  followed  by  another  wooden  plug,  after  the  extra  water  has  been 
circulated  out  of  the  way.  It  is  obvious  that  a  long  plug  in  the  tubing  may 
cause  trouble  in  circulating  out  extra  cement  in  case  the  formations  would 
take  no  more  cement. 

Plate  VIII  shows  a  crew  making  preparations  to  cement  off  bottom 
water  (through  tubing)  in  Wood  119  of  the  Arkansas  Natural  Gas  Company. 
Notice  both  low-pressure  and  high-pressure  pump  in  the  foreground. 

In  view  of  the  above  and  the  fact  that  2,200  feet  of  2-inch  tubing  will 
hold  only  about  forty-eight  sacks  of  cement,  it  would  seem  to  be  better  prac- 


Plate  VIM.     Preparing  to  Cement  Well  Under  Pressure  in  Bottom.     Arkansas 
Natural   Gas  Company,  Wood   No.  199,  Section  20-18-15,  p.  110. 


tice  to  omit  the  second  plug.  Then  enough  cement  can  be  kept  on  hand 
and  mixed  in  time  for  continuous  pumping  in  of  the  cement  necessary.  The 
tubing  should  be  kept  full  of  cement  until  no  more  can  be  forced  in,  ?fter 
which  the  circulating  valve  should  be  cracked  and  the  extra  cement  cir- 
culated out  between  the  outside  of  the  tubing  and  the  inside  of  the  casing, 
at  a  sufficient  speed  to  maintain  a  constant  pressure  on  the  cement  in  the 
well.  After  a  certain  point  is  reached,  the  action  of  the  pump  will  give  a 
good  idea  of  about  how  much  more  cement  will  be  taken.  It  is,  therefore, 
possible  to  reduce  the  waste  of  cement  by  starting  mud  or  water  into  the 
tubing  somewhat  before  the  end  point  is  reached.  The  cost  of  the  cement, 
however,  is  of  secondary  importance. 

Several  wells  in  the  El  Dorado  field  that  produced  bottom  water  have 
been  plugged  bv  cementing  through  tubing  under  pressure,  with  satisfac- 
tory results.  The  following  wells  were  plugged  either  under  the  super- 
vision or  at  the  request  of  the  State  Conservation  Department: 

1.  Foster    Oil    Company,    Hinson    No.    4,    was    plugged    with    cement 
(amount  unknown),  which  shut  off  the  water.    It  then  produced  clean  oil. 

2.  Guffey-Gillespie,  Steadman  No.  3,  was  plugged  with  cement  (amount 
unknown),  which  shut  off  water. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


3.  Standard    Oil    Company,    R.obertson    "B"    No.    3,    was    plugged    with 
thirteen  sacks  of  cement,  materially  reducing  the  production  of  water. 

4.  Busey,  Armstrong  No.  1,  was  plugged  with  ninety  sacks  of  cement 
and  shut  off  bottom  water.    This  well  has  been  abandoned. 

5.  Lucas  Tomberlin,  Crawford  No.  1,  was  plugged  with  eighteen  feet 
of  cement,  for  the  purpose  of  abandonment.     This  work  was   done  in  co- 
operation with  the  U.  S.  Bureau  of  Mines. 

6.  Magnolia  Petroleum,  Company,   McKinney  No.  3,  was  plugged  nine 
feet  with  cement,  but  the  plug  is  now  being  drilled  out.    This  well  produced 
oil  for  a  short  time  after  it  was  plugged.     The  cement  may  have  shut  off 
most  of  the  productive  portion  of  the  sand. 

7.  Constantin  Oil  &  Refining  Company,  Hill  No.  3,  was  plugged  with 
300  sacks  of  cement,  for  the  purpose  of  abandonment. 

8.  Arkansas   Natural   Gas   Company,   Wood   No.   199,   was   plugged  by 
stages  with  cement.     The  first  batch  of  160  sacks  filled  the  hole  only  two 
feet.    There  was  180  sacks  of  cement  next  pumped  in,  filling  the  hole  three 
and  one-half  feet.     Then  120  sacks  of  cement  was  pumped  in,  making  a 
total  of  460   sacks.     After  pumping  in  nine  wagon  loads  of  fine  sand  and 
empty  cement  sacks,  eighty  more  sacks  of  cement  was  added.     This  made 
a  total  of  540  sacks  of  cement.    Soon  after  this,  the  well  started  flowing  oil, 
but  it  soon  drew  in  water,  as  no  "chokes"  were  inserted  in  the  flow  line. 

This  well  is  reported  to  have  been  drilled  only  two  feet  below  the  top 
of  the  oil  sand.  When  first  opened  up,  it  produced  about  ten  days  through 
a  %-inch  choke.  The  rate  of  now  was  even  then  too  rapid,  for  large  quan- 
tities of  sand  and  water  were  expelled,  and  the  flow  was  finally  cut  off  by 
water.  Measurements  showed  the  well  had  drilled  itself  at  least 
two  feet  deeper.  Probably  it  had  drilled  itself  much  deeper  than 
the  measurements  indicated  and  had  subsequently  filled  in  with  loose 
sand.  The  well  is  no  doubt  located  where  edge  water  occurs  in  the  bot- 
tom of  the  main  oil  sand,  and,  therefore,  great  care  should  have  been  exer- 
cised in  regulating  its  flow.  The  fact  that  the  well  flowed  again  after  plug- 
ging, illustrates  the  point  that  plugs  are  beneficial  even  when  it  is  prob- 
able there  is  no  parting  between  the  oil  and  water.  If  this  well  had  been 
sufficiently  controlled  after  the  plugging,  there  is  little  doubt  that  it  would 
have  produced  considerable  oil. 

Some  wells  were  plugged  by  means  of  an  improvised  dump  bailer  with 
a  rod  attached  to  the  dart  for  dumping  the  cement.  This  method  was 
adopted  because  a  regular  dump  bailer  was  not  available.  The  washing  of 
the  cement  and  its  picking  up  in  the  return  of  the  bailer  to  the  surface 
were  minimized  by  first  attaching  only  a  few  feet  of  dump  rod.  Additional 
lengths  were  screwed  on,  as  the  cement  filled  up  the  hole.  The  idea  was 
to  have  the  bottom  of  the  bailer  dump  each  time  only  a  few  feet  above 
the  top  of  the  cement.  The  engineers  of  the  Bureau  of  Mines  worked  on 
the  abandonment  of  two  wells:  the  Abner  Davis,  Cornish  No.  1,  and  the 
Crosby  Syndicate,  Jackson  No.  1.  The  former  was  plugged  with  eight 
sacks  of  cement  which  filled  the  hole  about  sixty-six  feet,  and  the  latter 
was  plugged  up  sixteen  feet  with  cement. 

Operators  plugged  the  following  wells  by  dump  bailer  method,  result- 
ing in  increase  of  oil  production  and  decrease  of  water  production: 

Hickman  &  Baird,  McKinney   A-l,   plugged   six   feet   with  cement. 

Hickman  &  Baird,  McKinney  A-2,  plugged  three  feet  with  cement. 

Hickman  &  Baird,  McKinney  1,  plugged  nine  and  one-half  .feet  with 
cement. 

Hickman  &  Baird,  McKinney  3,  plugged  with  twenty  sacks  of  cement. 

White  Oil  Corporation,  Armstrong  N-2,  plugged  twenty-four  feet  with 
cement.  This  well  then  made  eighty-four  barrels  oil.  Drilled  out  one 
foot  at  a  time,  it  then  produced  water.  Plugged  back  second  time,  now 
pumping  sixty  barrels  oil,  no  water. 

White  Oil  Corporation,  Armstrong  S-l,  plugged  with  twenty  sacks 
cement  and  shut  off  bottom  water. 

It  has  been  repeatedly  proved  at  El  Dorado,  that  proner  plugging  will 
shut  off  or  materially  reduce  the  production  of  water,  and  because  this  is 
the  most  important  remedial  work  that  can  be  done  in  this  field  it  should 
be  concentrated  upon  by  operators. 

Some  of  the  operators  have  had  apparent  success  in  excluding  bottom 
water  by  tamping  empty  cement  sacks  in  the  bottom  of  the  hole  with  the 
drill  pipe.  The  sacks  are  rolled  tightly,  placed  in  the  top  of  the  drill  pipe 


40  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

and  are  then  forced  to  bottom  by  the  pump.  The  sacks  are  wedged  into  a 
very  compact  mass  by  "spudding"'  the  drill  pipe  on  them.  It  is  very  doubt- 
ful if  the  tamped  sacks  can  be  relied  on  to  permanently  retain  sufficient 
rigidity  to  hold  back  the  water.  The  apparent  success  may  be  only  tem- 
porary. Time  and  an  increasing  differential  between  the  water  pressure 
and  the  fluid  pressure  above  the  plug,  is  apt  to  wreck  such  a  plug. 

Handling  of  Cement: 

The  following  is  taken  in  part  from  "Engineers'  Survey  of  Burkbur- 
nett,"  Wichita  County,  Texas,  by  the  present  authors,  appearing  in  the  Oil 
&  Gas  Journal,  issues  March  24  to  April  20,  1922,  inclusive. 

Pure  cement  should  be  used  and  mixed  with  as  little  water  as  is  pos- 
sible for  handling  in  the  pump  or  bailer.  It  should  not  be  unnecessarily 
diluted  with  water  or  -with  mud,  after  it  is  placed  in  the  well.  Cement  is 
a  definite  mixture  of  compounds,  some  of  which  are  soluble  in  water.  The 
soluble  portions  should  hot  be  separated  from  the  insoluble.  Therefore,  a 
diluting  or  "washing"  of  the  cement  will  seriously,  if  not  wholly,  destroy 
its  hardening  qualities.  Likewise,  a  dilution  with  an  excess  of  other  ma- 
terial, such  as  mud,  will  reduce  its  strength. 

Cement  will  set  readily  under  salt  water  and  many  other  foul  or  highly 
mineralized  waters,  providing  sufficient  care  is  taken  in  handling  it. 

Ten  feet  of  settling  through  water  is  too  much  washing  for  a  small 
quantity  of  cement.  The  unsuccessful  use  of  the  ordinary  bailer  with  a 
rod  attached  to  the  dart,  which  adaptation  was  originally  designed  for 
dumping  drilling  water,  has  led  many  operators  to  assume  that  cement  will 
not  set  in  oil  field  water.  It  has  been  proven  that  the  dump  rod  is  the 
cause  of  many  failures,  due  to  the  washing  of  the  cement  while  settling 
through  the  water  from  the  dart  to  bottom. 

The  cement  should  be  placed  directly  from  the  bailer  at  the  bottom  0? 
^the  hole  with  as  little  agitation  as  possible.  This  can  be  done  by  a  suitable 

•  dump   bailer,    such  as   is   shown   in  Figure  2.     It  will   pay   an   operator  to 
possess  a  reliable  tool  of  this  kind,  if  he  expects  to  use  that  method  for 

-cementing  casings  or  for  plugging  off  bottom  water.  Some  of  the  patented 
•dump  bailers  are  dependable;  one  makes  trips  and  holds  the  valve  open 

"."by  means  of  a  latch  near  the  bottom. 

After  the  first  bailer  is  dumped,  care  should  always  be  taken  to  raise, 
the  bottom  of  the  bailer  to  the  top  of  the  cement  and  allow  ample  time 
for  draining  the  cement  from  the  bailer,  for,  otherwise,  the  cement  will 

•  drain  from  the  bailer  as  it  is  drawn  upward.     This  is  undesirable,  because 
it  means  a  considerable  settling  of  the  cement,  through  the  water.    It  should 

"be  made  certain  that  all  commotion,  such  as  action  of  gas  or  water,  is  elim- 
inated before  the  cement  is  placed,  or  very  shortly  thereafter. 

When  cement  can  be  made  to  bond  with  the  walls  of  the  hole,  there  is 
no  better  method  than  a  good  cementing  job  for  shutting  off  top  water  with 
casing  or  for  plugging  off  bottom  water.  When  handled  properly,  it  will 
set  under  nearly  all  conditions;  in  foul  water  and  in  oil.  Age,  moisture 
and  improper  storage  may  render  a  good  quality  of  cement  unfit  for  use. 
Failures  of  cement  to  set  in  oil  wells  have  resulted  from  poor  cement,  and 
these  can  probably  be  prevented  by  the  use  of  simple  tests  made  in  ad- 
vance. The  following  procedure  is  recommended:  Take  three  small  av- 
erage samples  of  the  cement;  mix  one  with  water  from  the  well,  and  the 
other  with  distilled  or  very  pure  water.  Place  the  stiffly  mixed  samples  in 
tall  containers  and  finish  filling  the  first  two  with  the  foul  water,  taking  care 
to  avoid  commotion  and  washing.  On  the  third  sample,  the  same  water 
may  be  added  to  the  container  that  was  mixed  with  the  cement.  After  a 
day  or  so,  notice  the  condition  of  the  samples.  If  none  of  them  have  set 
hard,  experiments  should  be  made  with  other  lots  of  cement  until  it  is 
certain  that  a  reliable  lot  has  been  found. 

It  is  common  practice,  in  some  fields  of  other  states,  to  use  from  100 
to  500  sacks  of  cement  and  to  pump  it  through  casings  with  or  without  the 
use  of  separating  plugs.  In  some  of  these  instances,  the  casings  have  been 
cemented  solid  with  cement  from  the  shoe  to  the  surface.  This  confines 
each  fluid  to  its  original  stratum,  assuming  the  cement  sets  hard  all  the 
way  and  completely  jackets  to  the  casing. 

The  advantages  of  using  large  quantities  of  cement  are: 

1.  When  the  mud  of  rotary  wells  cannot  be  washed  with  water,  on 
account  of  caving  formations,  the  first  cement  that  is  pumped  out  of  the 
shoe  scours  the  mud  from  the  lower  formations  and  casing.  This  allows 


EL,  DORADO,  ARK.,  OIL  AND  GAS  FIELD  41 

the  final  cement  to  properly  bond  with  them.  The  first  cement  will  not 
harden,  due  to  the  dilution  with  mud,  but  this  portion  will  be  on  top  and 
its  condition  will  not  affect  the  shut-off. 

2.  The  cement  may  seal  off  water  and   oil-bearing  strata  of  shallow 
depth.     In  the  case  of  rotary  wells,  it  will  prevent,  as  far  as  it  bonds  with 
casing  and  formation,  washing  of  the  absorbed  mud  and  establishment  of 
water  infiltration  into  oil  and  gas  deposits  that  lie  above  the  shoe. 

3.  The   casing  seat  will  have  additional  strength.     Large  amounts   of 
cement  have  been  used  to  hold  casings  that  could  not  be  supported  by  the 
formation  adjacent  to  the  shoe.     Also,  the  possibility  of  high-pressure  oil 
or  gas  blowing  past  the  shoe  and  outside  of  the  casing  is  lessened. 

4.  The    casings    are    protected    over   a    larger    surface    from    corrosive 
water.      The   mud   fluid  of  rotary   wells   is   also    good    protection,   provided 
water  does  not  wash  its  way  to  the  casing.     (See  also  No.  2.) 

5.  The  danger  of  collapsing  water  strings,  due  to  water  pressure,  is 
lessened  by  reinforcing  the  casing  on  the  bottom  where  the  greatest  pres- 
sure occurs.     When   cement  is  used   in  this   manner,  a  shallow  water  de- 
posit may  not  exert  as  high  a  maximum  pressure  on  the  casing  as  a  deeper 
water,  although  the  two  waters  would  stand  at  the  same  level.     Suppose, 
for  instance,  that  a  water  string  is  cemented  at  2,100  feet  and  that  a  good 
jacket  of  cement  extends  to  a  depth  of  1,500  feet.     If  no  water  exists  in 
the  formations  between  1,500  feet  and  2,100  feet,  the  top  water  cannot  exert 
a  pressure  at  a  point  lower  than  1,500  feet,  or  no  greater  than  about  700 
pounds   per  square  inch,  for  salt  water.     A  thin  jacket   of   cement  would 
suffice  to  prevent  this  water  from  following  down  the  casing  and  exerting 
the  full  hydrostatic  pressure  on  the  bottom  of  the  casing.    Assume  now  that 
a  water  stratum  exists  at  1.800  feet  and  that  this  water,  like  the  shallow 
water,  would  rise  to  the  surface  if  not  obstructed  by  the  cement.     It  will, 
therefore,   exert  a  pressure  of  about  850   pounds  per  square  inch  for  salt 
water.     When  high-head  water  is  sealed  with   cement  alone,   it  will  exert 
pressure  directly  on  the  cement  and  casing  so  that  thick  walls  of  cement 
will  be  necessary  to  lend  substantial  reinforcement  to  the  casing. 

The  final  necessity  of  thick  cement  walls  will  also  depend  upon  the 
rigidity  of  the  water  stratum  and  upon  the  amount  of  cement  that  hardened 
in  its  pore  spaces.  These  considerations,  and  the  possibility  of  low-head 
porous  strata  becoming  converted  to  high-head  by  secondary  water,  argue 
forcibly  for  thick  walls  of  cement  around  the  lower  portions  of  the  casings, 
especially  when  the  factor  of  safety  against  collapse  is  small.  When  cement 
is  used  in  rotary  wells,  this  feature  is  taken  care  of  usually,  as  the  water 
strings  have  a  large  clearance  in  most  cases. 

6.  When  the  water  in  the  hole  is  too  foul  to  allow  the  cement  to  set, 
an  excess  of  cement  mixed  with  good  water  may  displace  the  foul  water 
sufficiently  to  allow  hardening  for  a  certain  distance  above  the  shoe  . 

The  use  of  large  quantities  of  cement  may  appear  to  be  a  waste,  when 
considering  the  future  recovery  of  casings  in  the  process  of  repairs  or 
abandonment.  However,  a  portion  of  the  casing  is  a  small  item  compared 
to  the  total  cost  of  drilling  a  well,  and  is  very  small  compared  to  the  pos- 
sible waste  of  oil  and  gas  due  to  water  infiltration.  These  statements,  of 
course,  are  not  strictly  true  in  the  case  of  "wildcat"  wells,  where  under- 
ground conditions  and  possibilities  have  to  be  learned  first. 

Abandonment  of  Wells: 

It  is  always  expensive  and  sometimes  impossible  to  re-enter  and  re 
pair  an  improperly  abandoned  well,  and  for  those  reasons  it  is  highly  de- 
sirable to  use  particular  care  in  the  abandonment  operations.  In  this 
work,  each  fluid  near  the  oil  and  gas  horizons  should  be  confined,  as  far 
as  practicable,  to  its  own  stratum.  If  this  idea  is  followed,  the  recovery 
of  oil  and  gas  from  other  wells  will  be  increased  and,  at  the  same  time, 
valuable  deposits  of  potable  water  may  be  protected  from  contamination 
by  brines  or  sulphur  water. 

A  well  may  be  properly  drilled  and  tested,  but  prove  to  have  no  com- 
mercial production  of  oil.  If  such  a  well  is  not  properly  abandoned,  how- 
ever, it  may  allow  water  with  a  high  head  to  travel  across  the  formations 
to  neighboring  wells.  The  improper  abandonment  of  wells  in  proved  areas 
is  usually  inexcusable  and  constitutes  a  deplorable  crime  against  our 
natural  resources. 


42  EL,  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


Too  much  reliance  should  not  be  placed  on  an  entire  water  string  left 
in  a  well,  inasmuch  as  the  rotary-mud  protection  from  corrosion  may  be 
overcome  by  water  action  after  subsistence  of  the  mud,  unless  the  mud 
was  subjected  to  a  considerable  closed-in  pump  pressure. 

The  proper  use  of  cement  and  of  mud-laden  fluid  afford  the  best  means 
for  the  proper  abandonment  of  wells.  The  technique  of  properly  placing 
cement  has  been  discussed  previously.  The  use  of  cement  for  this  pur- 
pose usually  calls  for  a  study  of  the  fluid  content  of  the  different  forma- 
tions, the  probable  future  worth  of  present  non-commercial  deposits  and 
the  possible  danger  of  leaving  two  or  more  oil  strata  open  together  between 
cement  bridges. 

In  general,  an  adequate  cement  plug  should  be  placed  in  the  bottom  of 
the  hole,  if  necessary,  with  substantial  cement  bridges  between  each  pair 
of  water,  oil  or  gas  strata.  Obviously,  the  present  and  possible  future  con- 
ditions of  the  area  determine  the  size  and  extent  of  these  plugs.  The 
problem  would,  on  first  thought,  appear  to  be  simplified  by  cleaning  out 
the  well  to  bottom  and  filling  it  with  cement  to  a  considerable  distance 
above  the  oil  zone  or  po'ssible  oil  zones.  Such  would  be  the  case,  but  if 
the  hardness  of  the  cement  were  not  tested  at  the  vital  points,  efficiency 
of  the  work  would  not  be  assured.  When  a  well  has  many  showings  of  oil. 
with  no  intervening  water,  there  is  a  temptation  to  leave  some  of  the 
sands  open  together,  with  possibly  a  cement  bridge  below  the  bottom 
showing  and  one  above  the  top  oil  deposit.  If  water  appeared  in  one  of 
these,  the  other  sands  might  be  flooded  from  a  well  improperly  abandoned. 

In  general,  long  cement  plugs  and  bridges  should  be  set  opposite  oil 
sands  when  a  well  is  abandoned,  but  they  should  be  tested  for  hardness 
at  proper  depths  during  their  construction. 

The  proper  method  of  abandoning  wells  will  vary  somewhat  according 
to  local  conditions.  Mud  fluid  has  been  used  to  good  advantage  in  El  Dorado 
for  such  work.  The  well  should  first  be  cleaned  out  to  bottom,  mud 
pumped  through  the  tubing  or  extra  casing  which  is  then  lowered  nearly  to 
bottom.  The  mud  should  be  pumped  in  until  returns  of  mud  have  been 
established  at  the  surface,  for  several  hours.  The  casing  is  then  packed 
off  and  mud  forced  in  under  extra  pump  pressure,  using  as  much  heavy  mud 
as  possible.  t 

Some  formations  will  take  enormous  quantities  of  thick  mud.  It  is. 
therefore,  occasionally  found  expedient  to  introduce  sawdust,  chopped  rope 
or  straw,  etc.,  into  the  fluid,  in  order  to  assist  in  clogging  the  pore  spaces. 
After  the  lower  part  of  the  hole  is  well  mudded,  the  water  strings  can  be 
removed  and  mudding  continued  up  the  hole  by  moving  the  mudding  string 
upward  as  the  work  is  accomplished.  If  there  is  a  conductor  string,  this 
can  be  removed,  but  the  final  mudding  at  the  top  of  the  hole  should  also 
be  done  under  extra  pump  pressure  in  order  to  seal  off  the  top  water. 
Heavy  mud  which  is  free  from  grit  should  be  used  in  all  of  this  work.  The 
top  of  the  hole  should  be  protected  from  debris,  and  an  occasional  inspec- 
tion made  to  determine  whether  the  mud  has  receded,  in  which  event  more 
should  be  added  to  the  top  of  the  column. 

The  caving  and  bridging  of  formations,  as  the  casings  are  removed, 
should  be  avoided  as  far  as  possible,  in  order  to  be  sure  that  the  mud  gets 
into  all  porous  formations.  In  this  way,  each  fluid  can  be  kept  sealed  in 
its  original  stratum  and  a  reliable  abandonment  accomplished. 

Another  satisfactory  way  to  abandon  a  well  is  to  force  mud  into  the 
formations  under  considerable  pump  pressure  between  cement  plugs  and 
bridges.  If  only  the  usual  pressure  due  to  circulation,  or  weight  of  the 
mud,  is  used  for  filling  the  space  between  cement  bridges,  it  is  possible 
that  a  gradual  absorption  of  the  fluid  by  the  formation,  may  occur.  This 
would  tend  to  break  the  column  of  mud  between  the  bridges.  It  might  re- 
sult in  a  washing  of  the  mud  with  water  and  a  harmful  migration  of  one 
or  more  of  the  fluids  under  consideration.  It  is  obvious  that  this  "slack" 
between  bridges  cannot  be  taken  up  by  adding  more  mud  at  the  surface. 
A  slow  movement  of  mud  into  the  formation  may  easily  appear  to  be  no 
movement  at  all.  However,  as  time  elapses,  a  column  of  mud  may  un- 
dergo considerable  further  absorption. 

The  Conservation  Commission  of  Arkansas  requires  that  the  producing 
sands  be  protected  with  cement  and  that  the  hole  then  be  filled  to  the  sur- 


EL  DORADO.  ARK..  OIL  AND  GAS  FIELD  43 

lace  with  mud.  If  the  bottom  of  a  well  is  plugged  with  cement  to  a  point 
above  the  oil  sand,  and  thick  mud  is  then  filled  in  to  the  surface,  the  aban- 
donment would  most  likely  be  effective,  if  more  mud  could  be  added  in  case 
it  receded  down  the  hole.  It  is,  of  course,  quite  possible  that  a  portion  of 
the  mud  fluid  would  be  held  at  the  surface  by  the  bridging  of  caved  forma- 
tions, while  subsidence  took  place  below  that  point.  The  migration  of  oil, 
gas  or  water  might  then  occur  below  the  bridge.  In  introducing  mud  into 
a  well,  it  is  also  possible  to  fail  to  get  mud  into  all  parts  of  the  well,  on 
account  of  bridging  formation.  It  is  therefore  necessary  to  mud  a  well  with 
a  string  of  pipe,  starting  at  bottom  and  mudding  and  applying  pressure 
opposite  each  porous  formation  which  may  contaia  oil.  gas  or  potable 
water,  as  the  casing  is  raised. 


Protection  in  Case  of  Deeper  Production 

The  present  producing  zone  of  El  Dorado  has  been  definitely  assigned 
by  the  U.  S.  Geological  Survey,  to  the  Nacatoch  subdivision  of  the  Upper- 
Cretaceous  period.  It  is  the  history  of  some  neighboring  oil  fields  with 
Nacatoch  production  that  they  have  also  obtained  deeper  production  and 
it  may  be  that  deeper  production  will  be  found  at  El  Dorado.  This  paper 
deals  with  deeper  production,  only  in  connection  with  conservation.  With 
this  possibility  in  mind,  adequate  means  of  protecting  the  various  oil  de- 
posits should  be  considered  in  case  deeper  drilling  is  carried  on. 

If  a  commercial  quantity  of  deeper  oil  is  discovered,  there  would  be 
general  activity  toward  its  exploitation.  Either  oil  wells  would  be  deepened 
or  new  wells  drilled.  For  the  sake  of  convenience  in  discussion,  the  zones 
of  interest  will  be  designated  as  follows:  Zone  A,  above  a  depth  of  1,900 
feet  below  sea  level;  Zone  B,  present  productive  zone;  Zone  C,  hypothetical 
deeper  production.  Zones  B  and  C  would  be  produced  from  at  the  same 
time  and  through  the  same  or  separate  wells,  depending  upon  the  distance 
between  sands  and  the  character  and  content  of  the  intermediate  forma- 
tions. Suitable  methods  for  bringing  in  deeper  production  are  outlined 
below. 

1.  A  well  can  be  deepened  for  lower  production  (a)   by  cementing  the 
next  smaller  casing  just  above  the  new  production  and  producing  with  or 
without  a  liner;    (b)  by  recovering  all  possible  of  the  original  water  string, 
side-tracking  the  remainder  and  carrying  the  same  size  for  a  deeper  shut- 
off.      In  (a)  enough  cement  should  be  used  to  reach  above  the  shoe  of  the 
first   water   string;    in    (b)    the   discarded    casing   should    be    plugged    with 
cement  before  sidetracking  in  order  to  prevent  its  becoming  a  water  chan- 
nel, mud  should  be  forced  into  the  strata  under  an  extra  pump  pressure  of 
at  least  500  pounds  per  square  inch,  and  enough  cement  should  be  used  on 
the  deeper  casing  to  reach  at  least  300  feet  above  the  top  of  Zone  B.    Most 
of  the  present  water  strings  are  6-inch  and  plan  (.a)   would  reduce  the  hole 
to  4-inch,  or  smaller  if  a  liner  were  used.     Such  a  plan,  however,  may  be 
found  feasible.     The   general  disadvantages   of  reducing  the   hole   to   such 
small  size  are,  small  area  of  face  of  hole  for  oil  to  drain  to,  and  the  ex- 
cessive danger  of  sticking  tools,  bailer  or  tubing  and  the  difficulty  of  con- 
ducting fishing  operations  in  such  a  small  hole. 

Plan  (b)  may  not  prove  desirable  for  the  reason  that  it  niay  be  im- 
possible to  reclaim  more  than  1,200  feet  of  the  water  string  and  that  side- 
tracking with  rotary  may  prove  difficult. 

2.  New  wells  could  be  drilled  to  obtain  lower  production.     This  would 
involve  the  question  as  to  the  number  of  strings  of  casing  to  use.     With  a 
suitable   practice  already  established  for  production  at  the  present   depth, 
the  drilling  of  new  wells  for  deeper  production  can  be  done  as  follows:     (a) 
cement  about  170  feet  to  200  feet  of  10-inch  or  12%-inch  casing  (as  usual), 
cement  second  string  a  short  distance   above  Zone   b    (as  usual),  cement 
third  string  just  above  Zone  C,  using  enough  cement  to  reach  above  the 
shoe  of  the  next  string:      (b)   omit  the  second   string  of   (a),  put  at  least 
500  pounds  extra  pump  pressure  on  the  mud  and  cement  lower  string  of 
casing   with   enough   cement    to   reach    at    least    300   feet    above   the   top  of 
Zone  B. 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


By  the  methods  outlined  above,  adequate  protection  could  be  afforded 
the  several  oil  deposits.  The  cementing  should  be  carefully  done,  employ- 
ing the  best  practice  of  the  two-plug  system.  Method  (b)  has  the  advantage 
of  saving  a  string  of  casing. 

High  and  low-pressure  deposits  should  not  be  left  open  together  in  the 
same  well  on  account  of  probably  dissipation  of  the  high-pressure  into  the 
low-pressure  strata.  It  is  possible  that,  before  abandoning  the  wells,  Zones 
B  and  C  could  be  produced  simultaneously,  by  perforating  the  water  string 
with  a  long-knife  perforator  opposite  the  top  of  the  present  production 
(Zone  B).  The  cement  jacket  should  protect  this  oil  from  both  top  and 
lower  water.  If  such*was  not  the  case,  cement  could  be  forced  out  through 
the  perforation  by  means  of  a  bridge,  tubing  and  packing  head  and  produc- 
tion then  resumed  from  Zone  C,  or  tests  made  of  Zone  A. 


Production  Record 


Oil    Produced,   Proven   Acreage,   Well   Spacing: 

As  show'n  in  Table  No.  1,  the  El  Dorado  field  had  produced  something 
in  excess  of  10,000,000  barrels  of  oil  by  the  end  of  October,  1921.  These 
production  figures  are  shown  graphically  in  Figure  3  (in  pocket).  At  that 
date  there  were  about  460  producing  wells  and  an  estimated  proved  acreage 
of  oil  and  gas  territory  of  6,825.  The  average  spacing  was  about  fifteen 
acres  per  well. 

The  figures  on  proved  acreage  and  spacing  are  misleading,  however,  on 
account  of  some  2,000  acres  of  the  area  being  gas  bearing  to  a  high  degree, 
thus  rendering  it  undesirable  for  present  exploitation  for  oil.  This  leaves 
about  4,825  acres  of  territory  that  may  be  considered  as  proved  oil  terri- 
tory. Considering  the  oil  area  alone,  the  average  spacing  of  wells  at  the 
end  of  October,  1921,  was  about  10.3  acres  per  well  (average  of  670  feet  dis- 
tance). By  the  end  of  November,  the  average  spacing  for  the  entire  field 
had  decreased  to  approximately  8.8  acres  per  well  (619  feet  distant).  Com- 
pletions were  made  at  the  rate  of  about  eighteen  or  twenty  wells  per  week 
during  October  and  November,  1921. 

In  the  estimate  of  4,825  acres  of  proven  oil-producing  area,  100  acres 
were  assigned  to  Section  33-17-15.  This  may  be,  as  many  believe,  a  sep- 
arate structure  from  the  main  field  and  its  probable  further  development  is 
necessarily  omitted  from  the  accompanying  estimates. 

Section  17-18-15  has  been  drilled  more  intensively  than  any  other  sec- 
tion in  the  field.  By  December  1,  1921,  the  average  spacing  in  the  pro- 
ductive part  of  that  area  was  about  six  acres  per  well  (wells  511  feet  apart). 
There  are  small  tracts  in  this  and  other  sections  of  the  field  where  the 
spacing  will  approximate  three  acres  per  well  (362  feet  distance).  Plate 
IX  gives  an  idea  of  the  close  spacing  of  wells  near  the  southern  boun- 
dary of  Section  17-18-15. 

The  general  ruling  of  the  State  Conservation  Commission  provides  that 
interior  wells  shall  not  be  closer  together  than  400  feet,  and  that  wells 
shall  not  be  nearer  than  200  feet  to  property  lines.  In  the  case  of  so-called 
"sh<5e  string"  properties,  the  Commission  is  more  lenient,  and  may  con- 
sider a  group  of  properties  as  a  whole  and  stagger  the  wells.  An  average 
spacing  of  400  feet  allows  only  3.67  acres  per  well.  In  the  light  of  present 
information,  it  is  safe  to  say  this  spacing  is  undoubtedly  too  close. 

The  following  figures,  while  approximate,  are  presented  to  show  that, 
in  view  of  conditions  prevailing  at  El  Dorado,  an  average  spacing  of  seven 
acres  per  well  is  no  doubt  too  close,  for  this  field. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


46  EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD         

The  principal  factors  to  be  considered  in  estimating  the  proper  spacing 
are: 

(1)  Acreage — a  proven  oil  area  of  4,825  acres  has  been  estimated. 

(2)  Cost  of  Drilling — $15,000  is  taken  as  the  cost  of  drilling  and  equip- 
ping a  well,  including  its  pro-rated   general  lease  expense.     This  figure   is 
probably  too  low. 

(3)  Total    Production — From    the    production    data,    a    production    of 
20,640,000  barrels  is  assumed  for  the  present  proven  acreage  and  reservoir. 
It  is  assumed  that  the  wells  will  not  be  spaced  closer  than  ten  acres  per 
well  (average  spacing  as  of  October,  1921).     Guided  by  the  data  of  Cutler 
and  Clute*  for  other  fields,  it  is  assumed  that: 

9-acre  spacing  will  yield  per  well  95.0%  of  yield  for  19-acre  spacing 
8-acre  spacing  will  yield  per  well  89.5%  of  yield  for  10-acre  spacing 
7-acre  spacing  will  yield  per  well  84.0%  of  yield  for  10-acre  spacing 

(4)  Production  Cost — 35  cents  per  barrel  is  assumed  as   the  average 
cost  of  production  during  the  productive  life  of  the  field.     This  is  meant  to 
include  all  expenses  incurred  in  production,   and  includes   "overhead"  and 
general  charges.    This  figure  is  difficult  of  estimation  at  this  time. 

(5)  Lease  Prices — The   figure  of  $500  per  acre  for  the  average  price 
of  leases  is  based  on  rather  meager  data,  but  it  will  serve  for  general  pur- 
poses.    It  is  probably  low. 

(6)  Loss  of  Oil — As  indicated  by  Table  I,  the  loss  of  oil  at  El  Dorado 
may  be  as  high  as  12  per  cent.     The  figure  of  7  per  cent  is  no  doubt  low. 

(7)  Interest — A  total  of  21  per  cent  is  here  assumed,  regardless  of  the 
time  of  receiving  the  oil. 

(8)  Salvage— $1,000  per  well  is   meant  to  be   the  average  net   return 
from  sale  and  re-use  of  casing  and  surface  equipment. 

(9)  Price  of  Oil — $1.35  per  barrel  is  here  assumed.     The  future  price 
of  oil  is,  of  course,  a  matter  of  speculation. 

(10)  Royalty — 12%%,  which  leaves  the   selling  price  of   oil  to  be   re- 
ceived by  the  lessee  as  $1.18  per  barrel. 

The  following  estimates  (slide  rule  computation)  must  be  considered 
as  only  approximate.  They  at  least  prove  that  an  average  spacing  of  as 
low  as  four  acres  per  well,  is  unprofitable.  From  Plate  X  (in  pocket)  it  will 
be  seen  that  wells  with  an  initial  average  daily  production  of  480  barrels  the 
first  month,  will  produce  during  their  entire  life,  an  average  of  42,800  bar- 
rels. 

Ten   Acres   Per  Well 

4825  acres-v-10  acres=482  wells— 

482  wells  @  $15,000  drilling  and  equipment  cost $  7,230,000 

482  wells  @  42,800  bbls.  each,  20,640,000  bbls.  @  35c  production- 
cost  7,225,000 

4825  acres  @  $500  for  leases 2,412,000 

Loss  of  oil  (7%)  1,445,000  bbls.  @  $1.18 1.706,000 

Interest,  21%   of  investment , 3,900,000 


$22,473,000 

Oil  sold,  19,195,000  bbls.  @  $1.18 $22,640,000 

Salvage  of  casing  and  surface  equipment,  $1,000  per  well      482,000 

$23,122,000- 
22,473,000 


Cain $649.000 


*Cutler,  W.  W.,  and  Clute.  Walker  S.,  Relation  of  Drilling  Campaign  to 
Income  -from  Oil  Properties — Reports  of  1ni'csti(jations.  U.  S.  Bureau  of  Mines, 
August,  19*1. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 47 

Nine  Acres  Per  Well. 

4825  acres-^-9  acres—  536  wells — 

536  wells  @  $15,000  drilling  and  equipment  cost $  8,040,000 

536  wells  @  40,600  bbls.  each,  21,800,000  bbls.   @   35c  production 

cost    '. 7,640,000 

4825  acres  @  $500  for  leases 2,412,000 

Loss  of  oil  (7%)   1,525,000  bbls.  @  $1.18 1,800,000 

Interest,  21%   of  investment 4,175,000 


$24,067,000 

Oil  sold,  20,275,000  bbls.  &   $1.18 .- $23,920,000 

Salvage  of  casing  and  surface  equipment.  $1,000  per  well        536,000 


$24,456,000 
24,067,000 

Gain $389.000 

Eight  Acres  Per  Wei!. 

4825  acres-^8  acres=603  wells — 

603  wells  @  $15,000  drilling  and  equipment  cost $  9,045,000 

603  wells  @  38,300  bbls.  each,  23,100,000  bbls.   @   35c  production 

cost    8,090,000 

4825  acres  @  $500  for  leases 2,412,000 

Loss  of  oil   (7%)   1.616,000  bbls.  @   $1.18 1,907,000 

Interest,   roughly   21% 4,510,000 


$25,964,000 

Oil  sold,  21,484,000  bbls,  @  $1.18 $25,380,000 

Salvage  of  casing  and  surface  equipment,  $1.000  per  well        603,000 


$25,983,000 
25,964,000 

Gain $19,000 

.  :  Seven  Acres   Per  Well 

4825  acres^-7  acres=689  wells— 

689  wells  @  $15,000  drilling  and  equipment  cost $10,335,000 

689  wells  @  35,960  bbls.,  24,790.000  bbls,  @  35c  production  cost....     8,675,000 

4825  acres  @  $500  for  leases 2,412,000 

Loss  of  oil  (7%)  1,734,000  bbls.  @  $1.18 2,046,000 

Interest  about  21% 4,933,000 


$28,401,000 

Oil  sold.  23,056,000  bbls.,  @   $1.18 - ...$27,220,000 

Salvage  of  casing  and  surface  equipment,  $1,000  per 

well 689,000       27,909,000 


Loss $      492,000 

It  may  be  interesting  to  note  that  approximately  22,400,000  barrels  of 
oil  would  be  produced  with  the  following  factors: 

(1)  A  proven  acreage  of  4,825.     This  does  not  mean   that  extensions 
to  the  field  will  not  be  made. 

(2)  An  average  thickness  of  twelve  feet  for  the  saturated  portion  of 
the  reservoir  formation.     The  data  is  rather  meager  on  this  point. 

(3)  An   average    porosity  of   25   per   cent.     On   account   of  the   inco- 
herence of  the  sand, 'no  samples  have  been  obtained  on  which  porosity  tests 
could  be  made.     In  an  uncemented  sand,  the  porosity  may  be  rather  high. 

(4)  An  ultimate  recovery  of  20  per  cent  of  the  total  oil  underground 
Either  of  the  last  three  factors  or  the  production  from  the  4,825  acres. 

may  have  a  different  value,  in  which  case  one  or  more  of  the  other  factors 
would  be  affected. 


48  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

Several  factors  that  will  influence  the  spacing  of  wells,  are:  Possible 
profits  that  can  be  derived,  estimated  amount  of  oil  recoverable  with  differ- 
ent spacings,  porosity  and  size  of  grain  of  reservoir  formation,  gravity  of 
oil,  gas  pressure  and  depth.  The  relation  of  well  spacing  to  possible  profits 
derivable  from  production,  is  one  of  the  most  important  factors  and  has 
not,  in  general,  received  much  attention.  .  It  is  apparent  that  a  larger  ulti- 
mate net  profit  expected  on  operations  will  justify  a  larger  expenditure  by 
drilling  more  wells,  in  order  to  extract  more  oil  in  a  shorter  period,  thereby 
decreasing  the  total  interest  charges  on  the  money  invested.  Expected 
profits  can  easily  be  swallowed  up  when  close-spacing  is  used,  by  excessive 
total  cost  and  attendant  interest,  depreciation  and  amortization  charges. 

The  individual  productions  of  wells  vary  considerably  at  El  Dorado. 
The  records  show  that  numerous  wells  have  increased  their  production  tem- 
porarily at  different  points  during  the  general  decline  of  production.  This 
condition  is,  no  doubt,  due  primarily  to  sand  trouble.  After  a  well  frees 
itself  of  sand  or  is  cleaned  out,  the  production  usually  increases.  The  ac- 
cumulation of  sand  and  waxy  sediment  in  the  liner  or  screen,  or  the  lower 
portions  of  the  tubing,  may  seriously  retard  production. 

Like  most  oil  fields,  El  Dorado  has  some  so-called  "spotted"  territory. 
For  example,  a  well  of  2,200  barrels  initial  flow  was  located  in  the  midst 
of  small  producers.  Its  decline  was  abnormally  rapid,  however.  The  rock 
pressure  is  said  to  have  been  low  and  not  well  sustained,  and  it  was  ap- 
parently an  isolated  prolific  spot. 

Quality  of  Oil: 

Some  of  the  oil  runs  as  high  as  37.5  degrees  Baume  gravity.  It  averages 
about  35.5  degrees  Baume  gravity  and  is  placed  in  the  class  of  paraffin 
base  oils.  Analyses  from  various  parts  of  the  field  indicate  that  the  crude 
averages  about  31  per  cent  gasoline  and  15  per  cent  distillate.  The  sul- 
phur content  is  rather  large,  frequently  exceeding  one  per  cent. 

Surface  Wastage: 

In  developing  an  oil  field,  it  is  impossible  to  avoid  all  waste,  especially 
during  the  pioneer  period.  It  is  possible,  however,  to  curtail  waste  to  a 
greater  extent  than  is  usually  done.  There  is  much  oil  lost,  due  to  the 
rush  in  completing  wells  that  could  be  prevented  with  little  extra  time  and 
expense. 

Evaporation  losses  are  field  losses  that  will  probably  never  be  en- 
tirely eliminated,  but  remarkable  economy  can  be  effected.  Wiggins*  has 
shown  by  numerous  experiments  and  data  that  the  average  evaporation 
loss  for  the  Mid-Continent  fields  is  6.2  per  cent,  divided  among  the  va- 
rious operations  as  follows: 

APPORTIONMENT    OF   THE    EVAPORATION    LOSS    SUSTAINED    BY 

CRUDE  OIL  ON    ITS  JOURNEY    FROM   THE   WELL 

TO  THE    REFINERY 


Per  Cent  Volume  Evaporated  Source    of    Information 

Location  of  Loss —    Summer  Spring  Winter    Avg. 


Plow  tank  

1.2 

1.0 

0.8 

1.0 

Estimate  plus  test  on 

filling  lease  tank 

Tilling  lease  tank 

.     1.2 

1.0 

0.8 

1.0 

Test 

Lease   storage   

1.8 

1.4 

1.2 

1.5 

Test 

Gathering    

1.3 

0.9 

0.8 

1.0 

Test 

Transportation    .. 

1.2 

0.9 

0.8 

1.0 

Estimate  plus  tank 

tests 

Test  on  filling  large 

tank 

Tank  farm   

0.9 

0.7 

0.6 

0.7 

Test 

Total 

7.6 

5.9 

4.9 

6.2 

(By  addition) 

*Wiggins,  J.  H.,  Evaporation  Losses  of  Crude  Oil  in  Storage  in  the  Mid- 
Continent.  Bulletin  No.  200,  Bureau  of  Mines  (in  press).  Advance  chapters  in 
trade  journals. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


4!) 


The  conclusion  as  drawn  by  him  is:  "This  figure  of  6.2  per  cent  when 
applied  to  the  196,000,000  barrels  produced  in  the  Mid-Continent  fields 
shows  that  12,152,000  barrels  is  the  yearly  evaporation  bill.  In  gallons,  it 
equals  510,000,000,  which  is  just  about  the  total  gasoline  produced  by  the 
natural  gas-gasoline  industry  in  the  United  States  in  1919." 

Gasoline,  the  most  valuable  portion  of  the  crude,  sustains  the  entire 
loss,  and  the  money  value  lost  is  much  higher  than  the  6.2  per  cent  volume 
loss.  Wiggins  has  proved  that  air  contact  with,  and  movement  over,  the 
'surface  of  the  oil,  is  responsible  for  the  large  evaporation  losses.  If 
storage  tanks  have  covers  actually  tight  and  arrangement  is  made  to  relieve 
pressure  through  a  liquid  seal,  evaporation  will  be  greatly  reduced.  After 
a  tank  has  been  provided  with  a  tight  cover,  an  efficient  combination  safety 
valve  and  air  excluder  can  be  made  by  connecting  one  or  more  goose-neck 
pipes  to  the  cover  in  such  a  manner  that  about  four  inches  of  oil  or 
water  can  stand  in  the  bend.  Such  protection  will  pay  for  itself  in  a  short 
time,  even  though  the  producers'  loss  is  in  volume  only.  If  an  oil  is  of 
sufficiently  high  gravity  to  remain  in  the  top  price  division  after  loss  by 
evaporation,  the  producer  actually  loses  only  in  proportion  to  the  volume. 
The  refiner's  losses  are  in  gasoline. 

One  operator  at  El  Dorado  reports  that  7,000  barrels  of  oil  stored  in 
a  tank  with  a  steel  top  lost  4  degrees  Baume  gravity  in  six  months.  The 
gravity  was  decreased  from  36  to  32  degrees.  The  loss  in  barrels  of  oil 
was  not  ascertained. 


Table  5 

Table  5  gives  an  analysis  of  typical  El  Dorado  crude  oil,  made  in  the 
Pittsburgh  laboratory  of  the  Bureau  of  Mines: 


Specific  gravity,  0.852 

Per  cent  sulphur,  0.83 

Saybolt  Univeral  viscosity  at  70°  F. — 57.0 

Saybolt  Universal  viscosity  at  100°  F. — 46.6 


Baume  gravity,  34.30° 

Per  cent  water,  0.1 

Pour  test,  below  51  F. 


Distillation,  Bureau  of  Mines   Hempel    Method 


Air  distillation,  Barometer  749 

mm. 

First  drop,  31°  C.   (88^  F.) 

Per 

Sum 

Cloud 

Temperature 

cent 

per 

Sp.  Gr. 

°B                     test 

Temperature 

°C 

cut 

cent 

cut 

cut  Viscosity  °P. 

°i?' 

Up  to     50 

Up  to  122 

50  to     75 

4.5 

4.5 

0.680 

75.9 

122  to  167 

75  to  100 

4.2 

8.7 

.701 

69.7 

167  to  212 

100  to   125 

7.1 

15.8 

.722 

63.9 

212  to  257 

125   to  150 

6.2 

22.0 

.746 

57.7 

257  to  302 

l&O  to  175 

5.1 

27.1 

.772- 

51.3 

302  to  347 

175  to  200 

3.6 

30.7 

.795 

46.1 

347  to  392 

200  to  225 

3.5 

34.2 

.810 

42.8 

392  to  437 

225   to  250 

4.4 

38.6 

.823 

40.1 

437  to  482 

250  to  275 

5.1 

43.7 

.833 

38.1 

482  to  527 

Vacuum  distillation  at  40  mm. 


Up  to  200 
200  to  225 
225  to  250 
250  to  275 
275  to  300 


5.5 

6.5 


5.4 
4.6 


5.5 
12.0 
17.9 
23.3 

27.9 


.853 
.860 
.874 
.890 
.903 


34.1 
32.8 
30.2 
27.3 
25.0 


40 
45 

60 

81 

132 


Up  to  392 
392  to  437 
437  to  482 
482  to  527 
527  to  572 


Carbon  residue  of  residuum — 10.3%. 


Approximate   Summary 


Gasoline  and  naphtha 
Kerosene    ... 

Gas  oil  

Light  lubricating  disfliat 
Medium  lubricating  distillate 


Per 

cent. 
307 

Sp. 
Gr. 
0.735 

°B. 

60.5 

13  0 

.823 

40  1 

12.0 
;e  11.3 
late  :.  4.6 

.857 
.882 
.903 

33^4 

28.7 
25.0 

50  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

The  senior  author  developed  a  formula  in  1916,  for  use  in  estimating 
mixtures  of  light  and  heavy  oils  to  make  up  tank  car  shipments  of  a  cer- 
tain desired  gravity  and  to  use  a  minimum  of  light  oil  in  the  mixture. 
This  formula  was  developed  mathematically  and  assumes  that  there  is  no 
volume  shrinkage  after  two  oils  are  mixed. 

It  is  interesting  to  note  that  the  results  from  the  use  of  this  formula 
give  results  of  oil  lost  by  evaporation  which  check  closely  with  an  estimate 
of  J.  H.  Wiggins,  of  the  volume  lost  in  the  case  cited  above.  Mr.  Wiggins 
has  been  working  for  two  years  on  evaporation  losses  of  Mid-Continent 
crudes.  The  formula  is  as  follows: 

Ax  (Ba— Bx)    (Bs+130) 


(Bx— Bs)    (Ba+130)   +   (Ba— Bx)    (Bs+130) 

Where  "A"  is  amount  of  oil,  "B"  is  Baume  gravity  of  oil,  "a"'  refers  to  por- 
tion added,  "s"  refers  to  portion  at  start  and  "x"  refers  to  the  mixture.  In 
solving  the  problem  given  above,  it  can  be  assumed  that  70  degree  gasoline 
was  added  to  the  remaining  32  gravity  oil  to  make  up  7,000  barrels 
of  36  gravity  oil.  Assume  that  the  average  gravity  of  the  evaporated  por- 
tion was  70  degrees  (corresponds  to  oil  analyses).  Then  Ax=7,000,  Ba=70. 
Bs=32,  Bx=36.  Substituting  in  the  formula. 
7000X34X162 

As—  =6112  barrels. 

(4X200)    +    (34X162) 

which  was  the  amount  of  oil  remaining  after  evaporation.  The  amount 
evaporated  was  then  888  barrels,  or  12.7  per  cent.  The  efficiency  of  this 
cover  in  excluding  air  circulation  is  not  known  and  the  same  is  true  of  the 
determination  of  the  loss  of  gravity.  A  small  additional  expenditure  in 
proper  design  of  the  tank  cover  would  have  reduced  the  evaporation  losses 
greatly. 

Besides  evaporation,  there  has  been  a  great  deal  of  oil  lost  at  El  Dorado 
by  spray,  poor  separation  from  water,  inadequate  storage  for  uncontrolled 
wells,  seepage  and  fire.  Plate  XI  shows  a  rapidly  constructed  sump  for  an 
uncontrolled  well.  A  great  deal  of  oil  ran  along  the  natural  surface  drain- 


Plate  XI.     Waste  of  Oil   by  Storage   in   Earthen   Sump. 

age  channels,  where  much  of  it  was  lost  by  evaporation,  seepage  and  fire. 
Some  of  it  has  been  reclaimed  by  the  operating  companies  and  by  in- 
dividuals. The  oil  thus  reclaimed  by  impounding  and  skimming  has  usually 
lost  most  of  its  gasoline.  Because  of  the  recent  increase  in  the  price  of 
crude  oil,  operators  will,  no  doubt,  exert  more  effort  toward  conservation 
of  their  oil 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  51 

As  a  protection  against  the  spread  of  fire,  all  steel-storage  tanks 
should  each  be  surrounded  by  earthen  walls  of  suitable  height  and  distance 
from  the  tank.  Bowie*  gives  detailed  information  on  this  subect.  A  por- 


Plate  XII.  A  55,000-Barrel  Steel  Tank  on  the  Standard  Oil  Tank  Farm. 
Shows  Portion  of  Adequate  Fire  Wall  which  Centers  the  Tank  in  a  Closed 
Basin. 

tion  of  a  55,000-barrel  steel  tank  with  a  suitable  tire  wall  is  shown  in  Plate 
XII.  It  is  located  on  the  Standard  Oil  tank  farm  at  El  Dorado.  Such  tanks 
should  also  be  protected  by  a  complete  fire  foam  equipment. 

The  waste  of  gas  at  the  surface  has  not  been  unusually  large.  The 
principal  losses  have  occurred  from  blowing  wild.  In  certain  areas,  the 
gas  waste  may  be  sufficient  to  reduce  the  total  recovery  of  oil  by  ordinary 
methods.  If  gas  is  allowed  to  escape  in  large  quantities,  it  by-passes  oil 
in  the  sand  and  cuts  down  the  ultimate  recovery.  This  is  due  to  the  gas 
being  much  more  fluid  than  the  oil  and  it,  therefore,  encounters  less  re 
sistance  to  passage  through  the  reservoir.  The  sand  then  becomes  too  rap- 
idly impoverished  of  gas  and  the  oil  recovery  is  diminished. 

For  other  oil  fields,  production  statistics  and  physical  measurements 
of  underground  factors,  such  as  sand  thickness  and  porosity,  indicate  that 
there  is  always  more  oil  left  underground  that  is  raised  to  the  surface.  Es- 
timates of  the  total  recovery  of  oil  by  ordinary  means,  vary  from  10  per 
cent  to  40  per  cent  of  total  oil  underground.  With  this  in  mind,  it  is  not 
difficult  to  realize  how  necessary  it  is  to  consider  every  possible  means 
of  aiding  recovery.  A  few  additional  per  cent  of  ultimate  extraction  may 
represent  millions  of  barrels  of  oil. 
Production  of  Gas: 

As  pointed  out  previously,  there  are  about  2,000  acres  of  proved  gas 
producing  area  in  the  El  Dorado  field.  This  area  is  being  developed  Only 
enough  to  supply  the  local  needs  for  gas.  As  the  gas  is  depleted  from  the 
oil  deposits  of  the  same  strata,  tiiere  will  no  doubt  be  some  transfer  of  gas 
to  them  from  the  gas  area.  The  conservation  of  gas  is  urged,  therefore, 
as  it  may  assist  in  the  recovery  of  the  oil  in  adjacent  areas. 

An  estimation  of  the  total  amount  of  gas  used  and  wasted  is  not  at- 
tempted on  account  of  incomplete  information. 

Up  to  about  September  10,  1921. 
At  least  50  wells  had  been  completed  with  an  initial  open  flow  in  excess  of 

5,000,000  cubic  feet  of  gas  per  day; 
At  least  33  wells  had  been  completed  with  an  initial  open  flow  in  excess  of 

10,000,000  cubic  feet  of  gas  per  day; 


*  Bowie,  C.  P.,  Oil  Storage  Tanks  and  Reservoirs,  Bulletin  Xo.  7-55.  U,  S. 
Bureau  of  Alines.  1918.  Extinguishing  and  Preventing  Oil  and  Gas  I- ires,  Bulle- 
tin No,  179.  U.  S.  Bureau  of  .^fincs.  IQ^O. 


52 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


At  least  24  wells  had  been  completed  with  an  initial  open  flow  in  excess  of 
15,000,000  cubic  feet  of  gas  per  day; 

At  least  12  wells  had  been  completed  with  an  initial  open  flow  in  excess  of 

20,000,000  cubic  feet  of  gas  per  day; 
And   5   wells   had   been   completed   with  an   initial   open   flow   in   excess   of 

25,000,000  cubic  feet  of  gas  per  day. 

These  statistics,  together  with  Table  6,  will  give  some  idea  of  the  amount 
of  gas  that  has  been  available. 

Some  of  the  wells  show  very  rapid  decline  of  gas  production  and  pres- 
sure. Water  infiltration  has,  in  many  cases,  undoubtedly  been  a  factor  in 
shortening  the  life  of  these  wells. 

Table  6 

DECLINE   IN   GAS   PRESSURE  AND  PRODUCTION   OF  SOME  OF  THE   WELLS 

OF   EL   DORADO 

1  921 


WELL 

Section 

*  Completed 

V 

Rock  Pressure       Working        Open  Flow  Capacity 
Lbs.  per  Sq.  In.  ,    Pressure     Thousands  of  Cubic  Ft. 

"oj 
j3 

£ 

bi 

3 
< 

CO 

+j 
a 
a> 
m 

0 
rH 

G 
<D 

m 

c- 

N 

ti 
3 

< 

jo 

"G 
o> 
rf) 

^ 

I 

"3 

's 

£ 

ci 

CO 

CD 

rn 

o 

P. 

Cv 

00 

McCauldin  1  (?)  
Lacy  No  1 

31-17-15 

31-17-15 
6-18-15 
6-18-15 
36-17-16 
26-17-16 
31-17-15 
6-18-15 
1-18-16 
|12-18-16 

6-'21 
5-12-'21 
2-  8-'21 
8-ll-'21 

2-20-'21 
4-'20 

700 
960 

720 

600 

900 
960 

140 
115 
140 
140 
150 
480 
120 
110 
Ki 

120 
115 
140 
140 
150 
320 
120 
110 
led 


no 

115 
120 
120 
150 
315 
110 
110 

by 

100 
100 
100 
100 
115 
300 
90 
90 
salt 

90 
85 
85 
70 
115 
190 
80 
90 
wa 

90 

85 
70 
70 
115 
190 
70 
90 
ter 

35,000 
35,000 
25,000 
15,000 

13,000 
25,000 

31,000 
30,000 

18,  000|  15,000  13,500 
16,000|13,  000(13,000 
15,000  1  10,000  1   6,000 
10,000  1   6,000  1   5,000 
•2,500    2,500  1   1,500 
11,000  1  11,000  110,00'0 
15,000  1  15,  000|  13,000 
6,000|   6,000  1   6,000 
Dead 
Dead 

Chal  Daniels  
Woodly  et  al.,  1  
Miles  No.  1  
Heartstone  
Burns  No  1 

Reynolds  
"Home"  Well  
Constantin    

The  active  gas  wells  listed  above  are  blown  daily,  tri-weekly  or  weekly 
for  ten  or  fifteen  minutes,  for  the  purpose  of  freeing  them  of  water.  This 
procedure  has  probably  drilled  some  of  the  wells,  in  the  unconsolidated 
sand,  deeper,  which  may  increase  the  inflow  of  water.  As  the  gas  occurs 
on  the  higher  portions  of  the  structure,  edge-water  could  hardly  be  ex- 
pected to  appear  there  during  the  early  life  of  the  field.  The  blowing  of 
gas  wells  to  full  capacity  is  a  practice  that  should  be  reduced  to  the  min- 
imum whenever  possible.  If  water  is  not  already  present  in  some  cases, 
this  will  aid  in  drawing  it  in  rapidly.  When  wells  are  producing  gas  with 
a  large  quantity  of  water,  the  well  should  be  repaired  or  at  least  plugged 
high  enough  to  retard  the  inflow  of  water,  if  it  is  coming  through  the  gas 
sand. 

Besides  blowing  wells  to  free  them  of  accumulated  water,  they  are 
also  blown  "open"  to  ascertain  their  mechanical  condition,  to  clean  out  the 
pore  spaces  of  the  formation,  to  allow  the  wells  to  be  repaired,  and  to  make 
open-flow  tests.  Water  can  be  removed  from  gas  wells  by  a  gas  syphon 
line,  which  does  not  interrupt  the  gas  service  of  the  well.  There  is  some 
loss  of  gas  incurred  when  a  syphon  line  is  used,  but  the  amount  required  to 
lift  the  water  to  the  surface  is  relatively  small.  The  frequency  of  open 
flow  tests  can  well  be  deduced  by  a  study  of  the  data  of  pressure  readings 
and  calculation  of  capacities  therefrom.  When  a  well  must  be  blown,  it 
should  be  done  by  an  experienced  man  who  is  familiar  with  the  physical 
condition  of  that  well. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


The  National  Committee  on  Natural  Gas  Conservation  adopted  the  fol- 
lowing resolution  on  June  11,  1920: 

"Resolved,  That  the  practice  of  'blowing  heads'  off  wells  for 
long  periods  to  get  open-flow  tests  at  stated  intervals  be  discon- 
tinued. That  pressure  tests  by  closing  'side  gates'  or  the  use  of 
other  practical  measuring  schemes  be  used.  That  wells  should 
only  be  'blowed'  when  practical  men  know  it  to  be  necessary." 

El  Dorado  natural  gas  is  at  present  used  for  power,  lighting  and  heat- 
ing in  the  field,  by  the  local  refineries  and  industries  and  by  the  city  of 
El  Dorado.  The  El  Dorado  Natural  Gas  Company  distributes  most  of  the 
gas  and  reports  an  average  daily  consumption  of  about  19,500,000  cubic  feet. 
The  wells  are  drawn  on  to  about  20  per  cent  of  their  capacity. 

Some  tests  made  by  operating  companies  show  that  the  gravity  of  the 
casinghead  gas  varies  from  .74  to  .92  and  the  dry  gas  runs  about  .60.  Re- 
liable data  on  gasoline  content  of  the  gas  were  not  obtained. 

Production   Decline  Curves  for  Oil  Wells: 

The  production  records  of  practically  every  well  in  the  El  Dorado  field 
were  obtained  and  used  in  making  the  production  decline  and  future  pro- 
duction curves.  The  production  records  of  certain  individual  wells  were 
available,  but  in  general  the  average  production  per  well  of  each  group 
was  used.  On  most  producing  properties,  the  oil  from  several  wells  is 
run  into  the  same  tank.  Because  the  correct  water  content  may  not  have 
been  deducted  in  every  case  and  the  date  each  well  started  to  produce  was 
not  always  available,  there  may  be  some  inaccuracies  in  certain  of  the  rec- 
ords. However,  it  is  likely  that  these  inaccuracies  are  compensating.  Some 
records  .of  groups  of  wells  were  rejected  on  account  of  being  too  greatly- 
affected  by  the  unknown  flush  production  of  new  wells. 

The  production  figures  of  each  well,  or  average  of  a  group,  were  tabu- 
lated in  terms  of  average  barrels  per  day  by  months.  These  data,  as  shown 
in  Table  7,  include  October,  1921.  In  arranging  these  figures,  the  "mathe- 
matical method"  described  on  page  88  of  the  1921  Manual  for  the  Oil  and 

Table  7 

Estimated   Future  and    Ultimate   Production  for  an   Average   Well   in  the 
El    Dorado   Field. 


Estimated 

Remaining 

Life 

Well 
Months 

23 

22 
21 
20 
19 
18 
17 
16 
15 
14 
13 
12 
11 
10 


ii 

Est.  Average 

Daily    Prod. 

Per  Well 

Per  Month 

Barrels 

10,000 

4,600 

2.300 

1,250 

700 

420 

255 

165 

106 

74 

52 

37 

26 

19 

14.5 

11 

8.5 

6.5 

5 

4 

3.2 
2.6 


in 

Estimated 

Monthly' 

Production 

Ool.  11x30.4 

Barrels 

304,000 

139,840 

69,920 

38,000 

21,280 

12,768 

7,752 

5,016 

3,222 

2,250 

1,581 

1.125 

790 

578 

441 

334 

258 

198 

152 

122 

97 

79 

61 


IV 

Est.  Future 
Production 
of  Average 

Well 
Barrels 

305,864 

166,024 

96,104 

58,104 

36,824 

24,056 

16,304 

11,288 

8,065 

5,816 

4,235 

3,110 

2,320 

1,742 

1,301 

967 

708 

511 

359 

237 

140 

61 

0 


V 

Est.  Total 

Ultimate   Prod. 

of  Average  Wei 

Col.  III  +  IV 

Barrels 


609,864 

;?05,864 

166,024 

96,104 

58,104 

36,824 

24,056 

16,304 

11,287 

8,066 

5,816 

4,235 

3,110 

2,320 

1,742 

1,301 

966 

709 

511 

359 

237 

140 

61 


54  EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

Gas  Industry  (issued  by  the  Treasury  Department)  was  used.  W.  W.  Cut- 
ler, petroleum  engineer  of  the  Bureau  of  Mines,  co-operated  in  the  work  ot 
preparing  production  figures  for  El  Dorado. 

The  first  month's  production  of  each  well  or  group  was  tabulated  in 
the  column  whose  average  approximated  that  production,  and  subsequent 
monthly  productions  were  placed  in  successive  columns.  The  averages  of 
the  columns  were  then  taken  as  the  basis  for  the  average  production  de- 
cline curve  shown  in  Plate  XIII.  In  this  way,  the  old  wells  of  small  initial 
production  served  to  extend  the  curve  some  months  in  the  future.  This 
method  is  used  in  accordance  with  the  law  of  Beal  and  Lewis  (Bureau  of 
Mines),  which  states  that  when  wells  are  producing  under  similar  condi- 
tions and  have  the  same  present  rate  of  production,  they  will,  on  the  av- 
erage, decline  at  the  same  rate,  regardless  of  their  relative  ages.  In  ex- 
tending the  average  future  production  to  the  assumed  economic  limit  of 
two  barrels  per  day,  logarithmic  cross-section  paper  was  used.  The  curve 
was  straightened  and  projected  in  the  manner  described  in  the  Treasury 
Manual. 

When  wells  came  in  as  strong  gassers  and  made  very  little  oil  at  first, 
the  month  of  maximum  oil  production  was  assumed  as  the  first  month. 
There  were  not  many  cases  of  this  character. 

After  the  field  began  producing,  it  was  soon  evident  that  the  use  of 
"chokes"  was  advisable  and  their  use  became  general.  The  effect  of 
"chokes"  on  production  has  been,  of  course,  to  make  the  decline  more 
gradual.  This  is  accomplished  by  holding  back  the  oil  and  gas  from  a 
rapid  discharge  and  this,  in  turn,  delays  a  water-coning  effect  in  the  sand. 
The  average  decline  curve  is,  therefore,  somewhat  modified  by  this  factor 
during  the  flush  production  period. 

The  production  decline  curve  here  presented  was  constructed  mainly 
from  the  records  of  flowing  wells.  It  may  be  that  when  pumping  becomes 
the  common  method  of  operation  throughout  the  field,  the  production  de- 
cline curve  will  be  more  sustained. 

After  preparing  the  average  production  decline  curve,  the  records  were 
divided  into  groups:  (1)  those  of  wells  whose  first  month's  productions 
were  greater  than  500  barrels  per  day,  and  (2)  those  of  wells  whose  first 
month's  productions  were  greater  than  500  barrels  per  day.  This  showed 
that  both  large  and  small  wells  conformed  in  decline  with  the  average  pro- 
duction decline  curve.  Decline  curves  for  the  northern  and  southern  parts 
of  the  field  were  also  constructed,  but  were  so  near  alike  that  they  are 
omitted  and  only  the  average  curve  is  shown  in  Plate  XIII. 

Table  No.  7  is  based  on  the  average  production  decline  curve  shown 
in  Plate  XIII.  Column  II  shows  the  estimated  average  daily  production 
per  well  per  month.  The  figures  were  obtained  from  the  ordinates  of  the 
average  decline  curve  (Plate  XIII)  at  the  points  representing  the  various 
months.  For  any  particular  case,  these  figures  can  be  considered  as  first 
month's  production  or  as  the  production  of  any  other  month.  Column  III 
represents  the  corresponding  total  monthly  production,  the  figure  30.4  being 
used  as  the  average  number  of  days  in  a  month.  Column  IV  shows  the 
sum  of  the  monthly  production  subsequent  to  that  shown  in  Column  III,  if 
the  average  well  is  produced  down  to  an  assumed  economic  minimum  ot 
two  barrels  per  day. 

Column  V  is  the  sum  of  columns  III  and  IV  and  represents  the  sum  ol 
the  present  month's  total  production  and  the  estimated  future  production, 
of  an  average  well. 

It  is  likely  that  the  economic  limit  of  commercial  production  will  be 
somewhat  higher  than  for  most  oil  fields  on  account  of  the  large  quantities 
of  water  that  will" probably  have  to  be  lifted  with  the  oil.  Sand  trouble  is 
also  a  factor  that  may  cause  an  earlier  abandonment.  At  present,  many  of 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


the  small  producing  wells  are  off  production  a  large  part  of  the  time  on 
account  of  sand  troubles.  One  probable  compensating  feature  of  the  con- 
tinuous sand  movement  is  the  elimination  of  deposits  of  paraffin  and  other 
clOb'ging  material  on  the  walls  of  the  hole. 

It  must  not  be  inferred  from  Table  7  that  the  field  will  produce  com- 
mercially no  longer  than  twenty-three  months.  The  average  well  with  a 
first  month's  production  of  10,000  barrels,  for  instance,  will  produce  for 
twenty-three  months  to  an  economic  limit  of  two  barrels  per  day,  or  will 
produce  for  twenty-three  months  longer  after  it  has  declined  to  an  average 
monthly  production  of  10,000  barrels  per  day.  New  wells  may  be  drilled 
after  the  first  producers  are  abandoned  and  the  actual  life  of  the  field 
would  thus  be  extended.  The  curves  and  table  apply  to  the  present  pro- 
ducing oil  zone  only. 

The  curves  of  Plate  X  were  prepared  from  the  data  of  Table  No.  7  and 
are  for  the  purpose  of  interpolation  as  well  as  graphic  representation. 


Production  Methods 


When  drilling  in  high-pressure  gas  areas,  such  as  the  El  Dorado  field, 
it  is  essential  that  the  control  equipment  at  the  surface  be  of  sufficient 
strength  to  be  safe.  In  this  field,  special  valves  and  fittings  must  be  used, 
as  there  is  considerable  sand  produced  with  the  oil  and  the  wear  is  exces- 
sive. Plate  XIV  shows  a  steel  choke  badly  worn  by  sand. 


Plate    XIV.      A    Steel    Choke    Worn    by    the 
Passage  of   Sand  with  Oil. 


56 


EL  DORADO.  ARK..  OIL  AND  GAS   FIELD 


Safety   Devices: 

The  usual  casinghead  fittings  which  are  commonly  used  in  the  El  Do 
rado  field  (see  Plate  XV)  are  made  up  as  follows: 


Plate  XV.     "Christmas  Tree"   Equipment  of  About  Average   Design. 


(1)  Master  Valve — A  heavy  gate  valve  attached  to  the  6-inch  water 
string,  preferably  placed  below  the  derrick  floor  and  operated  by  an  exten- 
sion arm  in  case  of  emergency,  such  as  fire  or  blow-out.  In  order  to  ob- 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


57 


58  EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 

viate  the  danger  of  the  master  gate  being  blown  off  of  the  6-inch  pipe, 
clamps  and  tie  rods  are  used  as  shown  in  Plate  XV  and  Figure  4.  The 
lower  clamp  is  placed  below  a  collar  and  around  the  10-inch  conductor  pipe. 
These  clamps  consist  of  two  iron  bars  with  dimensions  of  about  one  inch 
by  six  inches  by  four  feet,  bolted  together  around  the  casing  and  connected 
by  tie  rods.  The  end  threads  allow  proper  adjustment  and  distribution  of 
the  strain  due  to  pressure. 

(2)  Control   Head — When   the  well   is   finished   with   cable   tools,   the 
drilling  should  be  done  through  the  master  valve  and  the  control  head.    In 
case  gas   becomes  bothersome   before  the   tools   are   removed,  the  control 
head  can  be  closed  on  the  line  and  a  reasonably  tight  seal  effected.    A  tee 
placed  between  the  master  valve  and  control  head  should  be  connectd  up 
and  in  readiness  for  delivering  oil  and  gas  or  lor  mudding  the  well  and 
killing  the  flow,  should  that  become  necessary.     When  the  wells  are  being 
finished   with   rotary  tools,   it  is  well   to   have   packing  clamps   or  a  blow- 
out preventer  in  readiness  for  emergency  when  removing  the  drill  stem.     By 
using  such  devices  and  paying  proper  attention  to  the  thickness  and  height 
of  the  mud  fluid,  wild  wells  should  not  occur,  except  in  cases  of  accident. 

(3)  "Christmas    Tree" — Above    the    master    valve    is    placed    a    cross 
from  which  lead  the  flow  lines  as  shown  in  rtate  XV.     These  lines  are  pro- 
vided with  gate  valves.    A  nipple  and  another  gate  valve  is  installed  above 
the  cross. 

Chokes  are  sometimes  placed  at  this  point,  but  they  are,  in  general, 
needed  only  on  the  separator.  The  chokes  are  cylindrical  steel  blocks, 
threaded  on  each  end,  with  their  length  about  twice  their  diameter  and 
having  a  small  hole  longitudinally  through  their  center.  Substantial  gate 
valves  are  placed  on  each  flow  line  for  the  purpose  of  shifting,  regulating 
or  stopping  the  flow. 

The  valves  and  fittings  used  in  El  Dorado  should  be  of  a  heavy  type, 
with  sufficient  margin  of  safety  over  the  field  pressure,  in  order  to  allow 
for  wear  and  abrasion  by  the  sand.  In  some  of  the  worst  sand  producing 
wells,  the  valves,  chokes  and  fittings  are  rapidly  worn  out,  unless  the  flow 
is  properly  controlled.  For  instance,  on  one  well,  a  6-inch  valve  seat  was 
ruined  in  half  an  hour.  Fittings  to  withstand  pressures  of  2,509  pounds 
per  square  inches  are  now  commonly  used. 

Oil,  Gas  and   Water  Separators: 

The  oil-gas-water  separators  in  common  use  at  El  Dorado,  consist  of 
about  seven  joints  of  10-inch  pipe  with  oil  and  gas  risers  at  each  end.  Fig- 
ure 4  shows  the  type  of  separator  generally  used  at  El  Dorado.  The  oil 
riser  at  the  higher  end  of  the  separator  consists  usually  of  two  4-inch  ver- 
tical nipples  about  6  feet  in  height,  each  having  at  the  top  a  4-way  tee 
connected  to  chokes  of  sizes  from  %  to  1  inch.  The  number  and  size  of 
chokes  used  will  depend  on  conditions.  Another  nipple  extends  from  a 
central  tee  and  connects  with  the  flow  line  to  storage.  The  chokes  are 
required  for  high-presure  wells,  in  order  to  lessen  the  flow  and  thus  reduce 
water  and  sand  trouble.  The  decrease  in  flow  by  the  use  of  chokes  tends 
to  prevent  the  formation  of  "cut  oil."  A  more  complete  separation  of  gas 
and  oil  is  accomplished  in  the  last  (high)  risers.  The  separator  is  gen- 
erally inclined,  being  about  six  feet  higher  at  the  end  farther  from  the 
well,  in  order  that  the  water  may  separate  readily  at  the  lower  end. 

For  the  purpose  of  bleeding  off  water  and  sand,  three  or  four  lateral 
6-inch  lines  of  three  joints  each  are  connected  on  the  under  side  and  near 
the  lower  end  of  the  10-inch  pipe  by  means  of  tees  or  welded  connections. 
The  opposite  ends  are  swedged  down,  so  that  2-inch  gate  valves  can  be 
used  for  regulating  the  flow  of  water.  The  bleeders  are  regulated  so  that 
each  will  carry  about  an  equal  distribution  of  water,  in  order  to  avoid  ex- 
cessive suction  action  on-  the  oil  in  the  separator  at  any  particular  point. 

Plates  XVI  and  XVII  show  the  water  being  discharged  from  sepa- 
rators. 

Some  of  the  operators  believe  that  emulsion  forms  after  a  mixture  of 
oil  and  water  passes  through  the  chokers,  due  to  the  expansion  of  gas.  If 
this  is  true,  it  is  desirable  to  have  a  sufficient  number  of  bleeders  to  draw 
off  as  much  free  water  as  possible  and  prevent  any  water  from  reaching 
the  chokers  at  the  end  of  the  separator.  It  is  never  possible  to  sep- 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 


59 


arate  all  the  water,  but  some  of  the  oil  is  freed  of  water  in  this  way  and 
the  amount  of  emulsion  which  can  form  is  thus  cut  down.  In  the  event 
of  emulsions  forming  before  the  oil  reaches  the  surface,  the  separators 
will  not  cut  down  that  which  had  already  been  formed,  but  may  assist  in 
preventing  the  formation  of  additional  emulsions.  The  exclusion  of  water 
is  the  only  certain  means  of  preventing  the  formation  of  emulsion,  although 


Plate  XVI.  Discharge  of  Water  and  Some  Oil  from  Separator.  Gas 
and  Oil  Risers  at  Ends  of  Separator  not  shown.  Some  Oil  being  Wasted 
with  the  Water  through  the  Bleeders. 


Plate   XVII.      Discharge    of   Water   from    Separator,    Clear   Water    being 
Discharged  from  the  Bleeders. 

when  the  gas  pressure  is  reduced,  gas  expansion  will  not  be  so  serious  a 
factor  in  forming  emulsified  oil.  The  large  quantities  of  gas  acompanying 
oil  in  the  El  Dorado  field  is  one  of  the  chief  factors  in  creating  an  intimate 
mixture  of  oil  and  water.  This  point  is  illustrated  by  the  action  of  fluid 
in  a  pumping  well  in  the  north  end  of  the  field.  The  superintendent  stated 
that  with  the  valve  on,  the  casinghead  open  (allowing  gas  to  escape)  no 
emulsion  was  produced.  With  that  valve  closed,  60  per  cent  emulsion  re- 
sulted. 


60  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

It  appears  likely  that  the  quantity  of  emulsion  formed  in  wells  with 
high  pressure  will  be  reduced  by  diminishing  the  output,  but  this,  if  true, 
would  not  be  of  economic  importance  in  all  instances.  For  example,  an 
operator  stated  that  the  production  of  one  well  making  16,700  barrels  per 
day  through  a  4-inch  flow  pipe,  was  reduced  to  3,400  barrels  per  day  by 
inserting  a  %-inch  choke. 

Dehydration: 

In  most  cases,  El  Dorado  oil  must  be  treated  after  it  leaves  the  sep- 
arator before  the  pipe  line  companies  will  accept  it.  At  least  four  gen- 
eral methods  of  treating  emulsion  have  been  tried  in  the  El  Dorado  field 
with  satisfactory  results:  They  are  (1)  the  Tret-O-Lite  System,  (2)  Cen- 
trifugal machines,  (3)  Electric  Dehydration,  (4)  the  so-called  "gun-barrel" 
tank. 

(1)  The  most  common  method  of  treating  emulsion  in  the  El  Dorado 
field  is  by  the  addition  of  chemical  compounds.     The  best  known  of  these 
is  Tret-O-Lite.     This  is  a  chemical  which,  when  mixed  with  some  oil-water 
emulsion,   causes  the   water  to  settle  out,   leaving   clean  oil.     The  cost  of 
treatment  varies  from  3  cents  to  18  cents  per  barrel  of  clean  oil,  according 
to  the  percentage  of  emulsion.     Tret-O-Lite  compounds  are  usually  under- 
stood to  be  essentially  crude  soaps  or  compounds  of  sodium  and  sulfonic 
acid.     The  average   cost   is   about   9   cents  per  barrel   of  oil  treated.     The 
amount  of  Tret-O-Lite  used  varies  from  10  to  70  gallons  to  every  1,000  bar- 
rels of  oil.     Different  methods  are  used  to  mix  the   Tret-O-Lite   with  the 
oil.     One  company  uses  about  1,000  feet  of  2-inch  coil  pipe  through  which 
the  emulsion  and  Tret-O-Lite  mixture  is  pumped  before  being  run  into  the 
settling  tank.     The   amount   of  Tret-O-Lite   running  into   the   coils    can   be 
gauged  by  means  of  a  glass  indicator,  before  the  mixing  occurs.     The  water 
settles  into  the  bottom  of  the  tank,  where  the  water  level  is  usually  kept 
about  seven  feet  from  bottom.     A  steam  pipe  open  at  its  lower  end  extends 
almost  to  the  bottom  of  the  tank  and  maintains  the  temperature  at  from 
100  degrees  to  110  degrees  Fahrenheit.     The  introduction  of  live  steam  into 
the  settling  tank  should,  however,  be  avoided,  because  it  agitates  the  oil, 
thereby  retarding  settling,  and  also  increases  evaporation.     The  clean  oil 
is  drawn  from  an  outlet  pipe  about  two  feet  from  the  top  of  the  tank  and 
runs  into  storage  tanks  by  gravity. 

One  company  uses  an  additional  device  to  insure  a  more  thorough  mix- 
ing of  the  chemicals  and  emulsion.  This  consists  of  two  joints  of  8-inch 
pipe,  about  forty  feet  long  and  laid  on  the  ground,  with  two  unjointed  pieces 
of  2-inch  perforated  pipe  placed  inside  from  each  end.  The  emulsion  and 
Tret-O-Lite  mixture  is  pumped  through  one  of  the  2-inch  pipes  and  inside 
the  8-inch  pipe  and  is  forced  out  through  perforations  in  the  other  small 
pipe.  The  more  uniform  mixture  is  then  pumped  through  coils  on  the 
ground,  to  increase  time  of  contact,  before  being  run  into  settling  tanks. 
Steam  coils  are  generally  used  to  raise  the  temperature  of  the  emulsion  to 
about  120°  Fahrenheit.  In  order  to  maintain  a  constant  feeding  pressure, 
it  has  been  found  desirable  to  feed  the  emulsion  from  the  stock  tank  into 
a  25-barrel  tank  at  about  the  same  level  as  the  pump.  By  this  method,  a 
reasonably  uniform  mixture  with  Tret-O-Lite  is  maintained. 

(2)  Centrifuge  System  is  used  to  some  extent  in  the  El  Dorado  field. 
Centrifuges  or  supercentrifuges,  as  the  oil  field  types  are  commonly  called, 
are  really  enlargements  of  the   cream  separator  with  certain  modifications 
which  adapt  them  to  oil  field  use.     They  rotate  at  speeds  which  reach  a 
maximum   of   17,500   revolutions    per   minute   and   develop    tremendous    sep- 
arating forces. 

In  the  El  Dorado  field  the  Magnolia  Petroleum  Company  has  installed 
a  5-unit  Sharpies  plant  for  treating  their  emulsions.  The  total  cost  of  in- 
stallation, including  equipment,  labor  and  freight,  is  approximately  $18,200. 
The  operating  cost  on  this  plant  is  not  known,  but  on  a  similar  plant  in 
another  field,  it  is  said  to  have  amounted  to  $62  per  day.  This  figure  is 
believed  to  be  the  minimum  cost  at  which  such  a  plant  could  be  operated, 
and  it  is  probable  that  such  a  low  average  could  not  be  expected  over  a 
great  length  of  time. 

In  this  installation  Tret-O-Lite  is  used  in  combination  with  the  cen- 
trifuge process  when  the  percentage  of  emulsion  is  greater  than  10.  The 
plant  is  5-unit  and  the  capacity  ranges  from  fifteen  to  twenty-five  barrels 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD 


61 


per  hour  for  each  machine  when  treating  oil* averaging  about  80  per  cent 
emulsion.  When  using  Tret-O-Lite  in  combination  with  the  centrifuge, 
four  quarts  are  used  to  100  barrels  fluid.  The  following  description  is  given 
in  a  report  by  the  Sharpies  Specialty  Company: 


Plate  XVIII.     The  Two-Unit  Electric  Dehvdrator  on  the  Hearin   Lease  of  the 
Humble  Oil   Company. 

"The  emulsion  is  pumped  from  storage  to  the  bottom  of  an  elevated 
supply  tank  which  is  equipped  with  a  steam  coil  and  Sarco  Regulator  for 
heating.  As  the  emulsion  enters  the  bottom  of  the  tank  it  rises  through 


62  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

such  salt  water  as  may  have  accumulated  from  the  emulsion  and  gradually 
nils  the  tank,  during  which  period  it  is  brought  up  to  a  standard  tempera- 
ture of  f'-om  160  to  170  degrees  Fahrenheit.  The  pre-treatment  of  emul- 
sion is  essential  and  in  fact,  some  emulsions  may  require  the  addition  of 
suitable  chemicals,  in  order  to  give  greater  plant  efficiency. 

(3)  The  Electric  Dehydrator — This  electrical  method  of  treating  emul- 
sions has  met  with  success  in  the  El  Dorado  field.     The  Humble  Oil  &  Re- 
fining Company  installed   a  two-unit   plant   in   the   south  part  of  the  field. 
This   installation   is   shown   in   Plate  XVIII.     On  account  of  the   high   per- 
centage of  B.  S.   (85  per  cent,  in  some  instances),  the  rate  of  recovery  of 
oil  was  below  normal  for  that  process,  the  average  capacity  for  ordinary 
emulsions   being  450  barrels  per  unit  per  day.     Tests   on  these  emulsions 
have  shown  that  they  average  about  68  per  cent  water. 

The  capacity  of  an  electrical  dehydrator  usually  varies  from  300  to 
1,200  barrels  per  day,  per  unit.  The  capacity  is  limited,  because  if  too 
much  emulsion  is  run  through  the  plant,  the  current  would  be  short-cir- 
cuited by  the  excessive  water  and  the  proper  separation  of  oil  and  water 
prevented.  The  emulsion  remaining  in  treated  oil  is  usually  less  than  one 
per  cent.  The  electrical  dehydrating  process  was  invented  by  Dr.  Fred- 
erick G.  Cottrell,  former  Director  of  the  Bureau  of  Mines.  The  Petroleum 
Rectifying  Company  gives  the  following  description  of  the  Electric  Dehy- 
drator: 

"The  Standard  Cottrell  apparatus  consists  essentially  of  the  electric 
treater  and  a  settling  or  trap  tank.  The  treater  is  approximately  three  feet 
in  diameter  and  ten  and  one-half  feet  high,  made  of  galvanized  iron,  this 
tank  shell  constituting  one  electrode  that  is  'grounded.'  The  other,  or  'live,' 
electrode  consists  of  several  circular  discs,  generally  four  discs  eight  inches 
apart,  mounted  on  a  vertical  shaft  concentric  with  the  treater  shell.  These 
are  slowly  revolved  by  gearing  from  a  small  moter.  This  electrode  carries 
a  voltage  of  approximately  11,000  and  is  properly  insulated  from  the  gear- 
ing and  the  rest  of  the  treater  *  *  *  *.  Within  the  treater  is  a  steam  coil 
for  controlling  the  temperature  of  the  emulsion  undergoing  treatment." 
(This  is  usually  about  135  degrees  Fahrenheit.) 

The  emulsion  is  run  through  an  electric  field  set  up  in  the  annular 
space  between  the  edges  of  the  discs  and  the  treater  shell,  where  it  is 
broken  up  by  the  electric  current.  The  water  forms  in  large  drops  and 
settles  to  the  bottom  by  gravity,  where  it  is  automatically  drawn  off  in  a 
continuous  stream.  The  clean  oil  rises  to  the  top  and  flows  out  to  the 
storage  tanks. 

The  electric  power-requirement  for  the  two-unit  installation  mentioned 
was  about  2.76  kilowatts.  The  probable  cost  of  generating  electricity  on 
the  lease  is  about  4  cents  per  K.  W.  H.,  making  a  total  cost  of  about  11 
cents  per  hour  for  the  electricity  needed  to  operate  the  two  units.  The 
total  cost  of  treating  oil,  considering  various  items  such  as  steam,  elec- 
tricity, royalty,  labor,  repairs,  interest  and  depreciation,  has  been  found 
to  be  from  one  to  three  cents  per  barrel  of  net  oil,  according  to  the  report 
issued  by  the  Petroleum  Rectifying  Company. 

(4)  The  so-called  "gun  barrel"  tank  which  is  sometimes  used  to  de- 
hydrate oil,  is  not  satisfactory  for  use  in  the  case  of  highly  emulsified  oil. 
It  is  suited  for  settling  out  water  held  more  loosely  in  suspension. 

The  apparatus  consists  essentially  of  a  tank  fitted  with  steam  coils  on 
the  bottom,  a  vertical  wooden  flume  from  top  to  bottom,  a  swing  pipe  con- 
nected near  the  bottom,  and  an  overflow  connection  near  the  top  of  the 
tank.  The  oil  is  run  into  the  flume  at  the  top.  It  is  conducted  to  the  bot- 
tom of  the  tank  and  comes  in  contact  with  the  hot  steam  cores  before  mixing 
with  the  other  fluid.  The  oil-water  mixture  is  broken  up  when  passing  up 
through  the  hot  fluid,  the  oil  rising  to  the  top  and  the  water  settling  to  the 
bottom.  The  clean  oil  runs  to  storage  through  the  overflow  pipe.  The 
height  of  the  water  can  be  regulated  by  raising  or  lowering  the  swing  pipe. 
The  excessive  heating  of  the  oil  by  this  process  results  in  considerable  loss 
by  evaporation. 

Natural   Gas  Gasoline: 

As  yet,  there  are  no  plants  for  the  recovery  of  natural  gasoline  at 
El  Dorado.  As  the  richness  of  gasoline  in  natural  gas  increases  as  the  gas 
pressure  decreases,  it  would  be  desirable  for  operators  who  produce  quan- 
tities of  gas  to  have  tests  made,  and  should  they  warrant  it,  install  gasoline 
plants.  One  operator  reports  that  he  extracts  a  portion  of  the  gasoline 
from  the  gas  in  a  unique  way.  Gas  is  blows  through  the  crude  oil  while 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


LE<j 


ELND 


a  Sucker  Rod* 

b  Wortinq    Barrel 

C  Collar 

J  iweoq*  N,ople 

e  St.nd.no    V.lvt 

f  ChoVt 

q  Per-forationj  m  Trap 

h  StHlinas 

>  Inlet   ?.pe 

j  Perforator  in  Liner 

C  Liner 

I  Tubtnq 

m  Tr.p 


FIGURE  V 


Fig.  5.     Sand  Trap  Used  in  Some  of  the  Pumping  Wells. 


64    EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 

in  a  tight  tank.    He  claims  gasoline  from  the  gas  is  absorbed  by  the  oil  and 
thus   silghtly  raises   the  gravity   of  the   crude.     In   some   cases,   a  compar- 
atively "dry"  gas  would  absorb  gasoline  from  a  fairly  light  gravity  oil. 
Types  of  Oil  Well   Pumps: 

In  the  El  Dorado  field,  oil  well  pumps  with  composition  cup  plungers 
are  most  commonly  used.  A  few  steel  plunger  pumps  have  been  tried  and 
have  gained  some  favor  for  handling  the  sand.  Several  companies  have 
used  a  home-made  sand  trap  successfully  in  this  field  in  combination  with 
the  ordinary  cup  pump  (see  Figure  5)  Instead  of  the  standing  valve  being 
placed  immediately  below  the  working  valve,  it  is  attached  to  a  stand  pipe, 
generally  %-inch  in  diameter.  This  stand  pipe,  which  is  also  the  inlet  pipe, 
is  screwed  into  a  choke  of  the  proper  size  and  threaded  to  receive  a  %- 
inch  pipe  on  both  ends.  The  lower  end  of  the  inlet  pipe  consists  of  about 
one  joint  of  a  %-inch  pipe  which  is  screwed  into  the  choke  below.  The 
choke  is  threaded  on  the  outside  so  that  it  may  be  inserted  between  two 
collars  on  the  trap.  The  trap  shell  is  usually  made  up  of  3-inch  pipe,  if 
for  use  with  2-inch  tubing.  The  choke  and  pipe  below  it  tend  to  prevent 
the  entrance  of  gas  into  the  working  barrel.  The  choke  also  serves  as  the 
bottom  of  the  second  or  upper  sand  trap.  The  oil  first  enters  the  liner 
through  perforations  (j),  then  flows  into  the  trap  (m),  through  perfora- 
tions (g)  just  below  the  choke  (f).  The  oil  passes  downward  between  the 
walls  of  the  trap  and  (^he  inlet  pipe  and  up  through  the  inlet  pipe  (i)  to 
the  standing  valve  (e).  Some  of  the  coarse  sand  drops  to  the  bottom  of 
the  trap  as  settlings  (h)  before  the  oil  enters  the  inlet  pipe.  In  case  the 
pump  stops  operating,  the  settling  sand  will  settle  past  the  standing  valve 
and  make  it  possible  to  resume  pumping  without  a  "wet  job."  These  traps 
must  be  pulled  and  cleaned  periodically,  but  they  are  known  to  reduce. the 
sand  trouble. 

A  great  many  kinds  of  pumps  designed  to  handle  sand  have  been  tried 
at  El  Dorado,  and  some  of  them  have  given  fair  satisfaction  under  the  try- 
ing conditions.  It  is  possible  that  a  combination  of  the  sand  trap  principle 
and  a  packed  steel  plunger  may  give  economical  service.  A  packing  gland 
at  the  top  of  the  pump  barrel  would  probably  lessen  the  amount  of  sand 
that  gets  between  the  plunger  and  barrel.  However,  it  is  not  always 
feasible  to  introduce  complicated  contrivances  into  wells.  Theoretically 
serviceable  pumps  may  prove  failures,  when  tried  out.  Much  sand  is 
pumped  with  the  oil  in  some  fields  of  the  United  States  and  it  is  not  un- 
reasonable to  expect  that  the  problem  may  be  solved  in  this  field.  Operators 
should  experiment  with  different  kinds  of  equipment  until  the  most  satis- 
factory pump  or  attachment  is  found. 

Pumps  equipped  with  composition  cups  have  generally  proved  more 
satisfactory  than  steel  plungers  for  pumping  sand-free  oil  of  light  gravity, 
on  account  of  the  pliability  of  the  cups,  which  allow  less  leak-back  of  low 
viscosity  oil.  The  cups,  however,  are  short-lived  when  considerable  coarse 
sand  is  produced. 

Regular  steel  sucker  rods  are  used  by  most  of  the  operating  companies 
in  El  Dorado  field.  At  least  two  concerns  use  wire  lines  instead  of  rods 
for  pumping.  Sinker  bars  are  used  just  above  the  pump  to  facilitate  the 
down  stroke.  The  use  of  lines  facilitates  the  pulling  of  cups  and  cuts 
down  the  production  expense  caused  by  pulling. 
Oil  Recovery  From  Unconso!idated  Sands: 

The  economical  removal  of  oil  from  incoherent  sands  will  vary  consid- 
erably with  several  factors.  The  viscosity  of  the  oil  is  one  of  the  main  con- 
ditions that  affect  the  problem.  It  is  necessary  to  remove  a  larger  quan- 
tity of  loose  sand  when  producing  heavy  oil  than  is  essential  for  producing 
light  oil.  The  heavy  oil  is  less  fluid  and  drags  more  sand  into  the  well 
with  it  than  does  light  oil.  It  is  sometimes  impossible  to  extract  heavy  oil 
without  also  lifting  large  quantities  of  sand. 

This  subject  has  been  discussed  at  length,  in  the  case  of  heavy  oils, 
by  Kobbe*  and  Suman.t  In  the  case  of  light  oil,  it  is  probably  better  to 
remove  only  enough  sand  with  the  oil  to  keep  the  oil  stratum  fairly  free 
from  mud  and  waxy  deposits. 


*Kot>be,  Wm.,  Recovering  Oil  from  Unconsolidatcd  Sands,  Vol.  LVI,  Trans- 
actions American  Institute  of  Mining  Engineers. 

"\Suman,  John  R.,  Petroleum  Production  Methods,  ft>.  282,  283. 


EL,  DORADO,  ARK.,  OIL  AND  GAS  FIELD  6u 

It  is  no  doubt  true  in  general  that  a  large  removal  of  sand  with  the  oil 
will  increase  the  extraction  of  oil  by  lessening  the  friction  offered  to  its 
reaching  the  well.  The  cost  of  handling  the  sand  must,  of  course,  be  a  large 
factor  in  determining  the  economical  procedure.  A  considerable  removal 
of  the  sand  with  the  oil  may  result  in  a  small  inverted  cone-shaped  cavity 
forming  at  the  well  and  in  a  slightly  decreased  density  of  sand  near  the 
well. 

The  overlying  formations  at  El  Dorado  appear  to  be  rather  loosely  con- 
solidated, with  the  exception  of  some  minor  lime  strata  and  the  roof  of 
the  oil  reservoir,  therefore,  may  not  stand  up  definitely  above  an  extensive 
cavity.  The  roof  may  generally  follow  the  sand  downward  and  maintain  a 
fairly  constant  sand  density,  or  it  may  stand  up  lor  a  while  and  suddenly 
collapse.  Such  collapse  of  .the  rock  overlying  the  oil  sand  has  been  known 
to  cause  serious  mechanical  difficulty  and  decrease  of  production  in  fields 
producing  heavy  oil. 

Experimentation  in  each  particular  area  or  field  is  the  only  reliable 
means  of  drawing  correct  conclusions,  but  in  view  of  the  known  conditions 
in  El  Dorado,  it  would  seem  inadvisable  to  remove  any  more  sand  than 
is  necessary  to  keep  the  sand  around  the  well  reasonably  clean.  Some  op- 
erators have  becDme  disgusted  with  screens  and  liners  and  have  allowed 
the  sand  to  "heave"  into  the  hole.  When  the  production  drops  off  consid- 
erably, tools  or  bailer  are  run  to  clean  out.  There  is  no.  definite  informa- 
tion at  hand  with  which  to  compare  the  effectiveness  of  this  practice  with 
the  use  of  liners  or  screens.  The  amount  of  open  hole  below  the  shoe  of 
the  water  string  would  influence  this  practice,  as  cavings  from  the  walls 
of  the  hole  may  be  a  serious  consideration  in  the  case  of  high  shut-offs. 

It  is  believed  that  the  gathering  of  clean  sand  around  a  liner  will  prob- 
ably not  offer  much  resistance  to  fluid  movement.  In  fact,  the  loose  sand 
should  be  the  more  porous  for  the  reason  that  it  has  no  cementing  material 
in  its  pore  spaces.  Clean  sand  does  not  clog  the  perforations  so  that  oil 
cannot  enter  the  liner,  even  though  it  bridges  in  them.  Perforations  up  to 
Vi-inch  have  been  used  in  the  El  Dorado  field. 

Perforated    Liners  and   Screen   Pipe: 

Perforated  liners  and  screen  pipe  have  been  used  in  various  ways  at 
El  Dorado.  A  home-made  screen  was  devised  by  close  wrapping  by  ma- 
chine of  No.  10  gauge  wire  around  a  perforated  pipe.  One  of  these,  after 
being  in  a  well  only  a  short  time,  became  plastered  over  with  fine  sand  and 
mud  which  shut  out  the  production.  Such  a  device  will  not  give  satisfac- 
tion unless  it  is  certain  that  no  impervious  material,  such  as  mud,  can  ac- 
cumulate on  it.  The  spaces  between  the  wire  wrappings  were  first  clogged 
with  fine  sand  and  then  with  mud.  Liners  with  inserted  screens  have  been 
tried  and  are  used  by  some  of  the  operators.  These  are  not,  in  general, 
satisfactory. 

Practically  all  screens  now  manufactured  have  a  wrapping  of  slots 
which  are  keystone-shaped,  in  order  to  minimize  the  wedging  of  sand  and 
pebbles  in  the  openings.  Two  makes  of  patented  screen  used  at  El  Dorado 
are  made  by  wrapping  "Keystone"  wire  around  and  soldering  the  wire  to 
perforated  pipe.  Another  make  has  slotted  "buttons"  inserted  flush  into 
large  perforations  in  the  pipe.  The  matter  of  selecting  a  suitable  size  for 
screen  mesh  must  be  given  considerable  attention  and  it  may  vary  some- 
what in  different  localities  of  the  field  and  in  any  well  as  the  gas  pressure 
declines.  The  size  of  the  openings  is,  of  course,  a  matter  of  experiment  in 
the  different  areas.  The  finer  meshes  of  screen  have  been  the  the  rule 
and  will  probably  continue  in  use,  as  long  as  screens  are  considered  useful. 

At  El  Dorado,  the  liners  and  screens,  when  inserted  very  far  below 
the  top  of  the  sand,  should  be  closed  on  the  bottom  to  prevent  the  sand 
and  mud  from  "heaving"  up  into  the  liner.  It  may  sometimes  be  advisable 
to  have  the  liner  or  screen  blank  for  a  certain  distance  above  the  bottom 
of  the  hole. 

Considerable  difference  of  opinion  exists  among  the  operators  regard- 
ing a  seal  for  the  top  of  the  liner.  Although  it  is  difficult  to  effect  a  tight 
mechanical  seal  between  a  liner  and  water  string,  it  is  not  difficult  to  ex- 
clude the  coarser  sand  by  that  means.  A  seal  may  also  be  of  service  in 
holding  the  liner  in  place.  In  one  case,  where  the  perforations  had  been 
clogged,  an  unsealed  liner  resulted  in  practically  all  of  the  oil  passing  up 


EL  DORADO.  ARK.,  OIL,  AND  GAS  FIELD 


between  the  liner  and  casing.  It'  a  liner  can  be  sealed  at  the  top  without 
bridging  sand  above  the  perforations,  it  would  be  good  practice  to  aid  in 
the  easy  removal  of  the  liner  when  necessary  to  clean  out.  A  canvas  packer 
is  used  at  the  top  of  the  liner  in  some  wells.  One  operator  has  decided  that 
the  best  system  is  to  use  a  perforated  liner  fitted  with  a  bell  nipple  on  top. 

It  is  believed  that  the  finer  sand  and  mud  content  of  the  oil  stratum 
should  be  allowed  to  have  fairly  free  entrance  into  the  wells,  in  order  that 
the  clogging  effect  will  be  reduced.  Any  tendency  of  this  oil  to  deposit 
paraffin  in  formation  or  tubing,  is  evidently  counteracted  by  the  scouring 
action  of  the  sand. 

In  the  declining  period  of  a  well's  life,  it  may  be  found  feasible  to  stim- 
ulate the  movement  of  fine  sand  and  sludge  through  the  liner  or  screen  and 
into  the  well.  Several  methods  are  known  for  stimulating  wells.  They  in- 
clude steaming,  positive  and,  negative  swabbing  and  the  introduction  of  hor 
oil.  Washing  with  hot  or  cold  water  is  sometimes  done  but  the  method 
should  be  used  writh  great  care,  if  at  all.  Excessive  water  is  not  beneficial. 
Hot  water,  put  in  from  the  surface,  may  drive  waxy  sediment  back  into  the 
sand  and  redeposit  them  along  a  ring  of  sufficient  cooling.  Vigorous  swab- 
bing is  not  recommended  on  account  of  the  ever  present  danger  of  draw- 
ing in  top,  edge  or  bottom  water  and  the  danger  of  caving-formations.  The 
use  of  hot  oil  or  distillate  is  probably  best  adapted  to  the  removal  of  any 
waxy  sediment  forming  under  conditions  as  found  at  El  Dorado.  The  in- 
troduction of  hot  oil  melts  the  waxy  sediment  and  also  tends  to  render  the 
oil  less  viscous  and  thus  permits  a  freer  movement  of  oil  sand  into  the 
well. 

If  an  abnormal  quantity  of  sand  flows  into  a  well,  it  may  become  neces- 
sary to  temporarily  raise  the  pump  to  prevent  its  sanding  up  or  cutting  out 
of  the  plunger. 

Flow  Oil  Through  Tubing: 

The  general  practice  at  El  Dorado  has  been  to  "flow"  wells  as  long  as 
they  could  produce  reasonably  large  quantities  of  oil  by  this  method.  Some 
of  them  flow  as  low  as  fifty  barrels  per  day  before  being  put  on  the  pump. 
A  few  operators  are  taking  advantage  of  the  gas  pressure  and  are  flow- 
ing the  oil  through  small  tubing  which  is  packed  off  at  the  surface  or  near 
the  shoe  of  the  water  string.  This  practice  is  economical  and  generally 
keeps  wells  flowing  for  an  additional  period.  Some  operators  put  their 
wells  on  the  pump  when  the  output  has  declined  to  100  barrels  per  day 
because  pumps  will  increase  the  production.  The  high  cost  of  pumping 
more  oil  with  large  quantities  of  sand  must  be  balanced  against  a  quicker 
return  on  the  investment,  but  has  the  advantage  of  better  protection  against 
drainage  by  neighboring  wells. 

Air  Lifts  for  Raising  Oil: 

Lifting  oil  by  means  of  compressed  air  jets  is  comi],>:u  practice-  in  som^ 
fields.  When  the  fluid  level  in  a  well  is  high,  due  principally  to  water,  any 
lowering  of  fluid  will  aid  in  the  recovery  of  oil,  as  discussed  under  Water 
Conditions.  Because  compressing  air  is  rather  expensive  and  because 
air  lifts  in  wells  tend  to  emulsify  oil,  the  method  may  not  always  be  adapt- 
able. The  production  of  water-free  sandy  oil  by  air  would  no  doubt  be 
economical  if  there  was  a  sufficient  quantity  of  oil  to  allow  of  fairly  con- 
tinuous operation.  The  efficient  lifting  of  liquids  by  compressed  air  calls 
for  about  35  per  cent  submergence,  which  would  not  be  likely  to  exist  for 
a  period  long  enough  to  justify  air  installations  to  produce  clean  oil.  In 
U.  S.  Bureau  of  Mines  Bulletin  195.  by  A.  W.  Ambrose  (referred  to  pre- 
viously), a  portion  of  an  unpublished  paper  i>v  E.  W.  \Vagy  gives  some 
interesting  data  on  compressed  air  lifting  practice,  to  which  the  reader  is 
referred. 

A  well  making  sufficient  water  to  cause  an  air  lift  to  appear  feasible, 
should  be  repaired,  if  possible,  in  order  to  increase  the  oil  production,  de- 
crease the  water  production  and  reduce  the  cost  oi"  lifting  so 'much  fluid, 
An  air  lift  must  operate  continuously  to  be  practicable.  When  water  is" 
shut  off,  pumping  of  oil  with  air  "by  heads"  is  not  practicable.  There  are 
so  many  factors  opposed  to  the  lifting  of  several  thou  and  barrels  of  water 
with  air.  in  order  to  obtain  several  hundred  barrels  of  oil,  that,  first  of  all. 
the  possibility  of  shutting  off  the  water  without  decreasing  the  oil  produc- 
tion should  be  considered.  In  other  fields,  much  water  was  produced  for 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 67 

several  years,  in  order  to  produce  some  oil,  after  which  the  water  was  shut 
off,  with  a  resulting  increase  in  oil  production.  Water  often  aggravates 
sand  trouble  by  settling  and  packing  the  sand.  Incoming  sand  will  not  be 
floated  out  by  a  water  current  as  well  as  by  an  oil  current  of  the  same 
velocity,  because  the  oil  is  more  viscous — it  has  more  "body." 

The  presence  of  dissolved  air  in  the  oil  and  gas  lowers  the  gravity  of 
the  oil  by  carrying  off  the  lighter  fractions.  Air  also  dilutes  the  gas  and 
may  ruin  it  for  fuel  use,  and  the  energy  necessary  to  extract  a  given  amount 
of  gasoline  from  gas  is  thereby  increased. 

The  air  lift  has  been  tried  in  only  a  few  wells  at  El  Dorado.  The  Clark 
&  Greer  well  on  Section  17-18-15  started  to  make  water  and  decreased  in 
oil  production.  The  well  was  put  on  air  and  the  oil  production  was  in- 
creased, due  no  doubt  to  a  lowering  of  the  fluid  level  in  the  hole.  Although 
several  thousand  barrels  of  fluid  per  day  was  removed,  the  fluid  level  was 
apparently  not  greatly  reduced.  The  water  soon  "killed"  the  gas  and  the 
oil  production  stopped.  Even  though  the  water  could  have  been  removed 
to  a  low  level  as  fast  as  it  entered  the  well,  its  steady  flow  through  the  oil 
stratum  would  have  prematurely  cut  off  the  oil  supply. 

Vacuum   Pumping: 

In  some  fields,  vacuum  pumps  are  applied  to  the  well  in  order  to  stimu- 
late production  and  to  enrich  the  casinghead  gas.  The  vacuum  pump  is 
attached  to  a  lead  line  from  the  casinghead  and  is  set  where  the  applica- 
tion of  power  is  convenient.  This  system  of  pumping  is  only  employed  in 
fields  where  the  production  has  declined  to  such  a  point  that  it  is  unprofit- 
able to  pump  the  wells  without  some  stimulation  of  production  or  an  en- 
richment and  increase  in  casinghead  gas. 

Although  vacuum  pumping  has  not  as  yet  been  tried  at  El  Dorado,  the 
subject  is  here  mentioned  as  of  possible  future  importance  in  that  field. 
Its  application  may  not  be  found  feasible,  but  if  used  it  should  be  applied 
cautiously  in  accordance  with  well-directed  experiments.  The  haphazard 
use  of  Vacuum  has  created  ill  feeling  among  operators  in  certain  fields. 
Vacuum  has  drawn  water  into  wells,  with  harmful  results. 

Regardless  of  the  generally  incoherent  condition  of  the  sand  at  El  Do- 
rado, vacuum  pumping  may  possibly  find  useful  application,  inasmuch  as 
a  suction  of  fourteen  pounds  per  square  inch  would  probably  influence 
sand  movement  no  more  than  a  positive  gas  pressure  of  fifty  or  one  hundred 
pounds  per  square  inch.  This  principle  does  not  apply  to  water  infiltration, 
however,  and  high  vacuums  may  rapidly  draw  in  water.  The  vacuum 
shown  on  the  gauge  at  the  surface  is  not  the  actual  vacuum  applied  to  the 
movement  of  oil,  as  friction  reduces  the  vacuum  by  the  time  it  is  applied 
to  the  sand.  In  applying  vacuum,  it  is  probably  best  to  start  with  a  low 
vacuum  and  increase  gradually.  Each  well,  however,  may  be  a  special 
problem.  It  is  reported  that  in  some  cases  high  vacuums  draw  less  oil 
than  low  ones,  and  wells  can  occasionally  be  increased  by  lowering  the 
vacuum  to  a  certain  point.  The  rapid  by  passing  and  loss  of  gas  reduces 
the  total  assistance  of  its  expansive  force  for  oil  extraction. 

•  It  is  sometimes  found  that  vacuum  pumping  does  not  materially  in- 
crease production.  When  the  productive  sand  is  coarse  and  heavy,  the 
wells  will  not  "sand  up"  so  readily  by  vacuum  pumping.  Some  very  di- 
verse phenomena  have  been  noted  under  apparently  similar  conditions  in 
vacuum  pumping.  There  is,  no  doubt,  much  to  be  learned  of  the  action  of 
vacuum  under  varying  underground  conditions.  While  the  use  of  vacuum 
pumping  will  increase  the  ultimate  extraction  of  oil  in  some  fields,  where 
conditions  are  suitable,  its  successful  application  is  doubtful  at  El  Dorado. 

Power  for   Pumping: 

The  power  most  extensively  used  in  the  El  Dorado  oil  field  for  pump- 
ing purposes  is  the  gas  engine.  Various  types  of  gas  engines  are  used. 
They  are  equipped  with  magneto,  "wyco"  and  hot  point  ignition  systems, 
which  are  discussed  under  the  subject  of  "Drilling  Methods."  The  steam 
engine  is  too  expensive  for  pumping  individual  wells,  unless  the  central 
power  of  a  jack  line  system  is  operated  by  that  means.  It  should  be  used 
in  such  a  manner  only  when  gas  engines,  oil  engines  and  electric  motors 
are  not  economically  usable. 

The  central  power  system  with  jacks  has  not  as  yet  been  installed  in 
the  El  Dorado  field.  The  use  of  jacks  is  usually  practicable  in  depleted 
fields  where  there  is  very  little  trouble  from  sand.  It  does  not  now  ap- 


6S  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

pear  likely  that  groups  of  wells  will  be  operated  by  jack  lines  from  cen- 
tral powers,  on  account  of  the  frequent  necessary  work  on  the  wells  clue 
to  sand  troubles.  If  this  condition  is  overcome  sufficiently,  jack  systems 
may  be  profitably  operated  in  conjunction  with  a  cheap  portable  power  unit 
for  pulling,  such  as  a  tractor  fitted  with  a  hoisting  drum,  or  even  by  in- 
dividual engines  which  are  left  at  the  well.  In  this  connection,  full  con- 
sideration must  be  given  to  the  probable  life  of  El  Dorado  wells.  If  the 
wells  produce  only  a  short  time,  it  might  not  pay  to  change  from  individual 
power  to  jacks.  In  general,  the  principal  factors  governing  the  selection 
of  suitable  pumping  systems  are  amount  of  production,  depth  of  wells,  size 
of  tubing,  gravity  of  oil,  topography  of  the  country,  relative  location  of  the 
wells  and  the  speed  of  pumping  desired. 

Counterbalances  and  Tail   Pumps    : 

Counterbalances  on  the  beams  of  pumping  wells  have  not  as  yet  been 
used  in  the  El  Dorado  field.  It  is  well  known  that  they  can  be  used  to 
advantage  in  any  field,  and  it  is  recommended  that  operators  install  them. 

Counterbalances  are  used  to  balance  the  dead  load  and  assist  in  main- 
taining uniform  turning  motion.  This  cuts  down  idle  time  due  to  parted 
rods.  The  primary  object  of  installing  them  is  to  decrease  the  power  con- 
sumption, idle  time  and  -rod  breakage.  Where  the  cost  of  gas  is  only  of 
secondary  importance,  suitable  counterbalance  will  soon  pay  for  itself  by 
decreasing  the  wear  on  the  gas  engine  and  rods.  The  counterbalance  also 
tends  to  reduce  the  amount  of  emulsion  in  production,  by  causing  the  rods 
to  move  more  smoothly.  Emulsion  is,  in  some  cases,  iormed  by  the  churn- 
ing action  produced  by  leak-backs  past  damaged  cups  and  valves  and  a 
portion  of  the  damage  is  due  to  the  vibration  of  the  rods. 

One  of  the  most  efficient  counterbalances  is  a  concrete  block,  supported 
from  an  extension  of  the  walking  beam  by  a  stirrup.  The  position  of  the 
stirrup  on  the  beam  may  be  changed,  in  order  that  the  leverage  may  suit 
the- conditions  of  the  load.  Guides  must  be  provided  to  prevent  tjie  con- 
crete block  from  swinging. 

Except  in  the  case  of  a  few  line  pumps,  beam-operated  pumps  have 
not  yet  been  installed.  The  tail  pump  is  usually  installed  between  the 
"sampson  post"  and  "pittman,"  or  on  an  extension  of  the  beam,  so  that  the 
same  power  pumping  the  well  operates  the  tail  pump.  The  upstroke  of  the 
tail  pump  is  actuated  by  the  weight  of  the  descending  rods,  but  its  down 
stroke  does  not  assist  in  the  lifting  of  the  rods.  Some  of  the  lead  lines  are 
long  and  the  frictional  resistance  is  considerable.  Some  flow  tanks  are 
considerably  higher  than  the  wells  and  additional  power  is  required  to 
force  oil  to  the  tank.  The  load  on  the  well  pump  can  be  appreciably  de- 
creased by  the  use  of  a  tail  pump  which  requires  little  or  no  extra  power 
to  operate. 


Conclusion 


In  studying  conditions  at  El  Dorado,  it  was  found  that  the  character  of 
the  reservoir  strata  is  somewhat  different  from  the  average  field.  With 
respect  to  the  association  of  oil  and  lower  water,  it  is  hoped  that  the  ideas 
expressed  herein  will  form  the  basis  of  continued  investigation  by  others. 
The  underground  relation  between  the  two  liquids  is  one  of  the  most  im- 
portant questions  to  solve.  Without  some  accurate  knowledge  on  this  sub- 
ject, the  handling  of  wells  becomes  largely  a  matter  of  guess  work.  "Cut 
and  try"  methods  are  necessary  to  gain  information  as  well  as  produc- 
tion, but  experiments  in  blowing  and  deepening  wells  should  not  go  beyond 
reasonable  limits.  The  drilling  and  production  practices  in  the  El  Dorado 
field  have  been  generally  wasteful,  much  of  which  could  have  been  avoided 
by  the  application  of  good  engineering. 

The  two  main  factors  affecting  the  recovery  of  oil  in  the  El  Dorado 
field  are  water  and  loose  sand.  Wells  that  make  considerable  lower  water 
should  be  plugged  in  the  b.ottom  with  cement,  regardless  of  whether  there 
is  a  known  impervious  parting  between  the  oil  and  bottom  water.  The  top 
of  the  plug  should  be  at  least  two  feet  above  the  probable  top  of  the  water. 
Best  results  with  cement  will  be  obtained  by  the  tubing  method,  under  a 


EL  DORADO,  ARK..  OIL  AND  GAS  FIELD  69 

pump  pressure  of  at  least  500  pounds  per  square  inch.  It  is  recommended 
that  a  wooden  plug  be  used  in  the  tubing  ahead  of  the  cement  and  that  a 
packing  head  with  a  relief  valve,  be  used  at  the  surface. 

At  El  Dorado,  rotary  drilling  has  failed  to  determine  the  safe  depth 
to  drill  wells.  Core-barrelling  has  been  unsuccessful  in  this  field,  on  account 
of  the  unconsolidated  character  of  the  oil  sand.  It  is  believed,  however, 
that  as  core-barreling  is  successful  in  soft  sands  in  other  fields,  that  bet- 
ter results  with  core  barrels  can  be  accomplished  at  El  Dorado.  It  is  rec- 
ommended to  drill  wells  in  with  cable  tools  after  cementing  the  water 
string.  The  driller  may  "feel  his  way"  into  the  sand  and  avoid  drilling  too 
deep. 

The  position  of  each  well  with  respect  to  the  structure  should  be  borne 
in  mind  and  down-dip  wells  with  a  contour-control  as  low  as  1,935  feet 
below  sea  level,  should  barely  penetrate  the  top  oil  stratum,  lest  the 
water-bearing  portions  of  the  strata  be  opened  up  after  producing  a  short 
time. 

The  problem  of  handling  sand  in  pumping  wells  may  be  solved  to  a 
great  extent  by  experimenting  with  steel  plunger  working  barrels  designed 
to  handle  sand  and  by  the  use  of  sand  traps.  The  control  of  flowing  wells 
is  a  matter  of  utmost  importance.  Wells  must  be  restricted  in  their  flow, 
in  order  to  avoid  "self  deepening"  and  premature  entry  of  water. 

Production  methods  used  by  various  operators  in  the  field  differ  widely. 
It  is  suggested  that  operators  study  the  results  obtained  by  other  pro- 
ducers who  are  trying  new  methods.  Informal  discussions  between  produc- 
tion men  of  the  various  companies  should  be  encouraged.  It  was  found 
that  some  operators  were  not  fully  informed  as  to  the  methods  in  success- 
ful use  by  their  neighbors. 

Uniform  systems  of  cost  accounting  should  be  adopted  in  order  to  cor- 
rectly compare  the  efficiencies  of  different  operations  and  appliances.  The 
free  exchange  of  ideas  and  open  discussion  in  a  spirit  of  co-operation  can- 
not fail  to  be  of  mutual  benefit. 

Sufficient  funds  should  be  provided  for  a  Conservation  Commission  com- 
posed of  experienced  and  competent  oil  men,  with  ability  to  cover  all  of 
the  important  inspection  work  of  the  field.  The  present  system  of  raising 
money  by  collecting  fees  is  inadequate  and  unsatisfactory.  The  amount  of 
money  necessary  to  support  an  adequate  conservation  force  will  be  insig- 
nificant as  compared  to  the  gain  to  the  industry. 

The  Commission  should  inspect  and  record  all  vital  operations  in  wells, 
such  as  test  of  water  shut-off,  special  mudding  operations,  plugging  bot- 
tom to  shut  off  water,  or  plugging  to  abandon.  Cement  plugs  should  be 
tested  for  hardness,  thickness,  and  location.  The  Commission  should  make 
underground  studies  and  render  decisions  in  writing  to  the  operators,  with 
respect  to  where  water  should  be  shut  off  and  the  depths  of  wells.  When 
the  companies  employ  engineers  to  study  underground  conditions,  they,  in 
consultation  with  the  state  representatives,  can  discuss  matters  of  dispute 
and  reach  satisfactory  and  logical  conclusions. 

Operators  should  welcome  such  a  plan,  as  they  would  be  protected 
from  flooding  with  water  by  inefficient  and  inexperienced  operators,  and  at 
the  same  time  there  should  be'  preserved  certain  valuable  facts  regarding 
the  wells  that  might  overwise  be  lost. 

The  possibility  of  shallower  and  deeper  oil  sands  of  importance  should 
be  considered  before  a  definite  plan  is  adopted  for  drilling  up  the  field.  As 
outlined  in  the  body  of  the  report,  the  proper  use  of  mud  fluid  and  cement 
is  recommended.  It  appears  logical  to  test  these  possibilities  before  aban- 
doning present  wells  on  account  of  depletion. 

Efforts  should  be  made  to  reduce  the  formation  of  emulsion  both  un- 
derground and  at  the  surface.  If  the  wells  and  pumps  are  in  good  me- 
chanical condition,  emulsions  will  not  form  so  readily.  Wells  that  flow 
water  with  oil  and  gas  are  likely  to  emulsify,  despite  all  efforts,  but  prop- 
erly designed  separators  will  aid  in  keeping  down  the  amount  of  emulsion 
formed. 

Swabbing  is  not  adaptable  to  El  Dorado  field,  because  of  the  loose 
sands.  It  should  be  limited  to  the  few  instances  where  wells  can  only  be 
rid  ol  mud  and  water  and  their  flow  started  by  swabbing. 

It  is  very  doubtful  if  vacuum  pumping  would  be  successful  at  El  Do- 
rado. 


70 EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 

The  spacing  of  wells  should  be  about  nine  acres  per  well  (627  feet  dis- 
tance i,  in  view  of  the  present  (November,  1921)  price  of  oil. 

Other  production  economies,  such  as  tail  pumps,  counterbalances,  mul- 
tiple pumping  with  jack  lines,  use  of  tubing  catchers,  use  of  low-pressure 
burners  to  conserve  the  rapidly  diminishing  gas  supply,  and  discard  of 
steam  power  or  proper  installation  and  insulation  of  boilers  and  steam  lines 
are  recommended  for  use  where  adaptable. 

Concerted  efforts  should  be  made  to  reduce  oil  losses  due  to  evapora- 
tion, seepage  and  other  mechanical  means.  Practically  no  gas  should  be 
allowed  to  waste.  Its  use  for  moving  oils  into  the  wells  and  its  use  for 
fuel,  render  it  highly  important  in  the  recovery  of  oil.  Surface  conserva- 
tion is  second  in  importance  only  to  underground  conservation. 


EL   DORADO.  ARK..  OIL  AND  GAS  FIELD  71 

El    Dorado  Oil  Field  in   Arkansas-Dis- 
covery and  Development 

The  El  Dorado  oil  field  in  Arkansas  was  discovered  by  the  Constantine 
Refining  Company  when  their  Armstrong  No.  1  well  in  Sec.  1,  T.  18  S.,  R. 
16  W.,  struck  an  immense  flow  of  gas,  estimated  at  40,000,000  cubic  feet 
a  day,  and  a  small  quantity  of  oil.  The  oil  men  of  the  mid-continent  region 
paid  comparatively  little  attention  to  this  discovery  for  several  months, 
although  a  few  companies,  acting  on  the  advice  of  geologists,  leased  some 
land  near  the  gas  well,  but  when  a  well  drilled  by  Mitchell  &  Busey  in  Sec. 
31_,  T.  17  S.,  R.  15  W.,  came  in  on  January  10,  1921.  with  a  flow  of  about 
1,500  barrels  of  oil  a  day  and  perhaps  ten  times  that  much  water,  there  was 
a  stampede  for  the  field.  Leasing  and  drilling  were  pushed  with  an  in- 
tensity so  tremendous  that,  in  spite -of  several  months'  delay  in  getting 
an  adequate  pipe  line  outlet  for  the  oil  produced,  the  field  was  developed 
with  remarkable  rapidity.  The  oil  sand  is  only  about  2,150  feet  below  the 
surface,  and  the  rocks  above  it  are  mostly  beds  of  shale  and  clay  that  are 
easily  penetrated  by  the  rotary  drill.  Wells  that  gave  a  large  output  were 
the  rule  rather  than  the  exception,  several  yielding  more  than  19,000  bar- 
rels a  day.  although  most  of  these  wells  produced  much  salt  water  with 
the  oil.  The  output  reached  about  82,000  barrels  a  day  during  the  week 
ending  August  20,  1921.  but  declined  rapidly  to  about  32,000  barrels  a  day 
during  the  week  ending  March  11,  1922.  Since  then  the  output  has  in- 
creased slightly. 

Studies  of  the  Geology  of  the   Field: 

Field  studies  of  the  geologic  structure  were  made  'in  the  summer  of 
1921  by  W.  W.  Rubey,  L.  G.  Mosburg  and  H.  W.  Hoots,  of  the  United  States 
Geological  Survey,  Department  of  the  Interior,  and  office  studies  were 
afterward  made  by  K.  C.  Heald  and  W.  W.  Rubey.  The  primary  purpose 
of  these  studies  was  to  learn  the  conditions  under  which  oil  is  most  likely 
to  occur  in  southern  Arkansas.  The  investigation  was  afterward  extended 
to  ascertain  the  relations  of  the  oil  to  the  water  in  the  strata  for  the  in- 
iormation  of  the  engineers  of  the  Bureau  of  Mines,  who  were  working  in 
co-operation  with  the  State. 

Each  oil-yielding  district  has  its  own  peculiarities,  and  the  rules  that 
may  guide  prospecting  in  one  area  may  not  apply  to  another.  The  great 
number  of  test  wells  that  have  been  drilled  in  southern  Arkansas  without 
finding  oil  in  large  quantity  except  in  the  El  Dorado  field,  show  either  that 
the  oil  pools  in  this  region  do  not  bear  the  same  relations  to  anticlinal 
structure  that  they  commonly  bear  elsewhere  in  the  mid-continent  oil  field 
or  that  geologists  have  not  learned  how  to  locate  the  anticlines  in  this 
field  by  studying  the  surface  formations.  If  the  geologist  is  without  definite 
rules  to  guide  him  in  discovering  oil  pools,  his  usefulness  is  much  less  than 
it  otherwise  would  be,  and  the  operator  must  hunt  for  new  pools  blindly, 
so  that  his  chances  of  success  will  be  reduced  and  the  average  outlay  for 
each  now  pool  he  may  find  will  be  greatly  increased.  Random  drilling  has 
discovered  many  great  oil  fields,  and  persistent  prospecting  without  geo- 
logic guidance  would  ultimately  find  every  pool,  just  as  a  blind-folded  man 
could  find  almost  any  object  he  sought  if  he  sought  long  enough,  but  this 
is  no  reason  why  the  blindfold  should  not  be  removed  if  it  can  be  removed. 
One  of  the  most  effective  aids  in  locating  undiscovered  pools  is  an  accu- 
rate, thorough  knowledge  of  the  conditions  in  fields  that  have  been  de- 
veloped, and  any  one  who  hopes  to  find  new  pools  in  southern  Arkansas 
should  study  the  El  Dorado  field  and  the  fields  to  the  south  in  Louisiana. 

Structure  of  the   Field: 

The  geologic  structure  of  the  El  Dorado  field  is  unlike  that  of  any 
other  known  field  of  similar  size.  The  studies  made  covered  only  the 
northern  part  of  the  producing  area,  but  there  is  no  reason  to  think  that 
the  structure  of  the  southern  part  is  materially  different.  If  the  sand, 
clay  and  gumbo  could  be  stripped  off  the  producing  bed  in  the  area  cov- 
ered by  the  map  no  large  dome  or  great  anticlinal  arch  would  be  seen.  The 
surface  of  the  oil  sand  is  so  nearly  level  that  it  might  remind  one  of  gently 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


R.15W. 


Structure  contours  on  top  of 
Nacatoch  sand  Cashed  lines, 
>  position  inferredihachurer; 
line  indicates  structural  depres- 
sion. Contour  interval  lOfeet 
Datum  is  mean  sea  level 


Depth  below  sea  level  of  cap  rock  above 
middlt  of  pay  sTreSk.MacatOCh 

sano 


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U.  &  GEOLOGICAL  SURVEY 

GEOLOGIC  STRUCTUHE  OF  NORTHERN  PART  OF  EL  DORADO  OIL  FIELD.  ARKANSAS 

BY  t  C  HEALD  AND  W.  W  RUBEY 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  73 


rolling  prairies  or  of  meadows  made  up  in  part  of  smoothly  rounded  knolls 
and  swales  or  hollows  whose  slopes  rise  in  even,  sweeping  curves.  The 
evenness  is  interrupted  by  a  number  of  low,  almost  vertical  cliffs  that  mark 
faults  where  the  rock  has  been  broken  and  one  side  of  the  break  has  risen 
from  one  to  thirty  feet  above  the  other.  There  are  probably  a  great 
many  more  of  these  breaks  than  are  shown  on  the  map.  Almost  without 
exception  they  trend  northeastward,  forming  a  sharp  angle  with  the  longer 
axis  of  the  field,  and  most  of  the  low  folds  that  vary  the  flatness  of  the  sur- 
face of  the  oil  sands  also  trend  northeastward. 

The  oil  sand  rises  higher  in  Sec.  1,  T.  18  S.,  R.  16  W.,  than  elsewhere 
in  the  part  of  the  field  that  has  been  mapped.  Not  enough  wells  have  been 
drilled  in  this  part  of  the  field  to  enable  the  geologist  to  work  out  its  struc- 
ture in  detail,  but  it  seems  more  nearly  anticlinal  than  the  narrow  oil- 
yielding  area  that  borders  it  on  the  northeast,  east,  and  southeast.  The 
few  well  records  available  indicate  that  in  this  part  of  the  field  there  is 
a  real  dome  on  which  the  beds  dip  gently  to  the  east  and  more  abruptly 
to  west  and  southwest.  The  wells  on  the  dome  yield  gas  and  a  little  oil. 
Between  this  dome  and  the  oil-yielding  belt  to  the  east  there  is  a  rather 
broad  area  over  which  the  structure  has  not  been  worked  out,  so  that  the 
impression  of  flatness  in  that  area  given  by  the  map  is  unjustified. 

The  structure  in  the  area  west  and  south  of  the  gas-yielding  dome,  in 
Sec.  1.  is  not  known,  but  the  few  records  that  are  available  show  that  the 
oil  sand  there  is  fully  as  high  as  it  is  in  the  productive  pr.rt  of  the  oil 
field. 

A  study  of  well  records  in  areas  east  and  west  of  the  El  Dorado  field 
shows^that  this  field  is  not  upon  a  pronounced  regional  uplift,  although  there 
may  be~a  slight  bulge  or  gentle  arch  in  the  El  Dorado  region.  The  strata 
dip  gently  to  the  east  and  southeast  over  most  of  southern  Arkansas.  If 
the  El  Dorado  field  is  on  a  regional  bulge  or  uplift  there  is  a  synclinal  de- 
pression west  or  northwest  of  it.  A  flattening  of  the  regional  dip  was  de- 
tected but  no  true  syncline.  Furthermore,  if  the  field  were  an  uplift  the 
strata  immediately  east  of  it  would  probably  show  steeper  dips  than  are 
common  in  this  region,  but  no  suggestion  of  such  steep  dips  was  found. 
The  location  of  this  field  is  therefore  not  controlled  by  the  manner  in  which 
the  rocks  are  folded.  There  is  no  true  major  anticline  here,  and  the  minor 
folds  did  not  control  the  distribution  of  the  oil,  although  the  gas  in  this 
pool  does  tend  to  concentrate  in  arched  or  domed  areas.  The  parts  of  the 
field  in  which,  as  shown  by  the  map,  the  structure  is  anticlinal  lie  in  a 
sinuous  belt  that  trends  in  general  northward  through  the  center  of  Sec  31, 
T.  17  S.,  R.  15  W.,  including  about  40  acres  in  the  NW%,  Sec.  5.  T.  18  S.. 
R.  15  W. ;  about  60  acres  in  the  northeast  corner  of  the  same  section:  about 
60  acres  in  the  north-central  part  of  Sec.  8,  T.  18  S.,  R.  15  W.;  and  about 
100  acres  in  the  southeast  corner  of  Sec.  7.  T.  18  S.,  R.  15  W.,  besides  the 
gas-yielding  dome  in  Sec.  1,  T.  18  S.,  R.  16  W.  In  no  one  of  these  areas 
are  there  oil  wells  that  show  productivity  above  the  average  or  the  free- 
dom from  water  trouble  that  might  be  expected  if  the  segregation  of  oil 
were  controlled  by  anticlinal  structure.  If  the  dates  of  completion  and  of 
average  decline  in  initial  production  are  taken  into  consideration  in  order 
to  compensate  for  interference  from  adjacent  producers,  the  wells  in  these 
anticlinal  areas  are  perhaps  a  little  above  the  average  for  the  entire  field, 
but  this  initial  production  is  not  higher  than  that  of  wells  in  adjoining  syn- 
clinal areas. 

On  the  other  hand  it  can  not  be  said  that  in  this  field  there  is  no  rela- 
tion between  geologic  structure  and  the  accumulation  of  oil,  for  structure 
includes  both  folds  and  faults,  and  the  faults  were  probably  influential  in 
forming  the  pool.  Nearly  every  area  of  high  productivity  in  the  oil-yielding 
belt  here  considered  is  traversed  by  one  or  more  faults.  A  ftrip  of  richly 
productive  territory  does  not  border  each  fault  shown  on  the  man,  but 
here  and  there  along  almost  every  fault  there  is  a  spot  of  unusual  rich- 
ness. 

The  direction  and  arranegment  of  the  faults,  and  the  shapes  of  the 
low  folds  that  accompany  some  of  them,  probably  indicate  the  presence  of 
a  large  fault  or  zone  of  faulting  in  the  beds  deep  below  the  Nacatoch  sand, 
trending  about  N.  15°  \V.  The  structure  shown  by  the  oil  sand  there  must 
have  been  produced  by  lateral  movement  along  this  fault,  the  strata  east 
of  it  moving  northward  relative 'to  the  strata  west  of  it. 


EL  DORADO.  ARK.,  OIL  AND  GAS  FIELD 


How  the  Pool  Was  Formed: 

The  Marlbrook  marl  is  believed  to  be  the  source  of  the  oil  in  this  field, 
and  the  accumulation  of  enough  oil  in  the  Nacatoch  above  the  Marlbrook  to 
form  a  commercial  field  is  probably  due  to  a  happy  association  of  a  source 
of  oil,  channels  through  which  it  could  migrate,  and  a  good  reservoir  bed. 
Oil  was  probably  not  formed  everywhere  in  the  Marlbrook,  at  least  not  in 
great  volume,  but  in  favored  spots  where  it  was  laid  down  in  shallow 
water,  and  possibly  raised  above  the  sea  from  time  to  time,  the  conditions 
were  right  for  the  deposition  and  preservation  of  oil-forming  matter.  In 
any  event,  in  some  places  the  Marlbrook  appears  to  have  supplied  large 
amounts  of  oil  to  the  overlying  Nacatoch  sand,  and  in  others,  where  the 
structure  is  seemingly  quite  as  favorable,  it  has  supplied  little  or  none.  At 
El  Dorado  the  zone  of  faults  crossed  a  productive  area  in  the  marl.  The 
oil  moved  up  along  the  fault  planes  and  accumulated  in  the  upper  part  of 
the  Nacatoch  sand.  Pronounced  anticlinal  folding  and  faulting  and  a  rich 
spot  in  the  Marlbrook  would  together  have  produced  ideal  conditions  for 
the  accumulation  of  oil,  and  under  such  conditions  the  water  trouble  that 
has  been  the  curse  of  the  El  Dorado  field  would  not  have  appeared.  The 
beds  of  sandstone  lie  so  flat,  however,  that  the  oil  they  contain  does  not 
saturate  them  to  any  great  thickness;  but  instead  it  is  found  in  thin 
layers  at  the  tops  of  several  beds  in  the  upper  part  of  the  Nacatoch,  and 
the  remaining  parts  of  these  beds  are  filled  with  salt  water.  The  gas  being 
more  mobile  than  the  oil  has  migrated  to  the  more  prominent  domes  and 
has  excluded  most  of  the  oil  and  the  water  from  certain  thin  beds  of  sand- 
stone under  the  arched  areas. 

If  the  formations  just  above  the  Nacatoch  had  contained  porous  sand- 
stones the  oil,  as  it  moved  upward  along  the  fault  planes,  would  probably 
have  formed  small  pools  in  them,  for  the  faults  are  not  limited  to  the  beds 
below  the  top  of  the  Nacatoch,  but  certainly  cut  the  Arkadelphia  clays, 
although  these  beds  contain  few  sands.  The  faults  may  cut  also  the  Mid- 
way beds,  although  this  supposition  can  not  be  definitely  verified  by  the 
well  records,  but  no  evidence  was  found  to  indicate  that  they  cut  the 
Wilcox. 

Instead  of  originating  in  the  Marlbrook  the  oil  possibly  may  come  from 
a  much  deeper  formation,  such  as  the  Brownstown  marl,  the  Eagle  Ford 
shale,  or  the  Lower  Cretaceous  beds.  The  depth  of  these  formations  below 
the  Nacatoch  is  no  obstacle  to  the  migration  of  the  oil,  for  the  faulting 
that  cuts  the  Marlbrook  must  also  cut  them,  and  if  it  could  furnish  chan- 
nels for  upward  migration  from  the  Marlbrook  to  the  Nacatoch  it  could 
almost  as  easily  furnish  channels  for  migration  from  the  deeper  beds.  If 
the  oil  came  from  the  Brownstown  marl,  there  may  be  chances  of  finding 
oil  reservoir  beds  in  this  formation  or  adjacent  to  it,  and  if  it  came  from 
the  Eagle  Ford  shale  there  is  a  good  chance  of  obtaining  it  from  the  Blos- 
som and  Woodbine  sands. 

If  the  oil  came  from  the  Marlbrook  marl,  however,  the  chances  of  ob- 
taining it  from  underlying  formations  are  not  exceptionally  good,  although 
these  lower  formations  should  not  be  utterly  condemned.  The  records  of 
other  fields  that  draw  oil  from  Upper  Cretaceous  formations  prohibit  such 
a  blanket  condemnation,  for  practically  all  fields  that  have  yielded  either  oil 
or  gas  in  notable  amounts  from  the  Nacatoch  sand  and  have  yielded  much 
greater  amounts  from  either  the  Blossom  or  the  Woodbine  sands,  or  both. 
The  lack  of  anticlinal  structure  at  El  Dorado,  however,  offsets  this  favorable 
feature.  WThere  oil  is  found  in  the  Blossom  or  the  Woodbine  there  is 
either  pronounced  regional  uplift  or  strong  anticlinal  folding.  In  the  Caddo 
and  De  Soto-Red  River  districts  there  are  both.  In  the  El  Dorado  district 
there  is  neither.  The  conditions  that  are  associated  with  oil  pools  in 
northern  Louisiana,  and  to  which  the  formation  of  those  pools  is  presum- 
ably due,  are  therefore  lacking  here,  and  production  from  the  deep  beds 
can  not  be  counted  on.  Nevertheless,  the  deep  sands  should  be  tested.  The 
most  promising  locality  for  a  deep  test  well,  so  far  as  the  map  shows,  is  on 
the  west  side  of  the  gas-yielding  dome  in  Sec.  1,  T.  18  S.,  R.  16  W.  The 
very  center  of  the  section  seems  to  be  a  good  location  for  such  a  test  well, 
but  as  it  is  desirable  to  make  a  test  for  oil  in  the  Nacatoch  at  a  place 
west  of  the  gas-bearing  area,  a  location  800  feet  west  of  the  center  of  the 
section  would  probably  be  preferable. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  75 

Oil  and  Gas  Above  the  Principal  "Pay"  Sand: 

A  few  wells  in  the  El  Dorado  field  have  reported  "showings"  of  oil  or 
gas  in  beds  in  the  Midway  formation.  The  few  reports  that  traces  of  oil 
have  been  found  in  these  beds  might  be  discredited,  for  enough  oil  to  give 
a  rainbow-colored  film  on  the  drilling  water  might  accidentally  get  into  a 
well,  but  not  traces  of  gas,  and  it  therefore  seems  evident  that  at  least 
one  bed  in  the  Midway  formation  carries  some  oil  and  gas.  This  bed  may 
lie  about  1,150  feet  below  the  surface  over  most  of  the  field,  or  about  970 
feet  above  the  Nacatoch  sand.  A  number  of  sands  in  a  zone  200-300  feet 
thick  may  carry  this  shallow  oil.  The  wells  in  which  it  is  reported  do  not 
lie  on  any  of  the  faults  that  have  been  mapped  or  very  near  them,  a  fact 
which  indicates  that  the  oil  probably  did  not  rise  along  those  faults. 

Reported  showings  of  oil  or  gas  in  a  number  of  wells  that  have  been 
drilled  within  a  radius  of  forty  miles  of  the  El  Dorado  field  suggest  that  an 
oil-bearing  sand  may  lie  at  the  base  of  the  Midway  formation,  which  in  the 
El  Dorado  field  is  from  575  to  625  feet  above  the  Nacatoch.  No  careful 
tests  of  these  shallow  beds  seem  to  have  been  made  in  the  field,  in  spite 
of  the  very  apparent  need  for  such  tests.  Small  water-free  wells  that  would 
draw  oil  from  a  bed  not  more  than  1,200  feet  below  the  surface  would  prob- 
ably yield  greater  net  profits  than  the  more  spectacular  but  less  reliable 
wells  that  get  oil  from  the  underlying  Nacatoch  sand.  Tests  of  the  shallow 
sands  should  be  made  very  carefully,  for  the  gas  in  them  is  evidently 
low  pressure,  and  it  would  be  easy  for  one  to  drill  through  a  thin  oil  or 
gas-bearing  sand  without  suspecting  its  presence. 

Possible   Extensions  of  the  Field. 

In  the  part  of  the  field  covered  by  this  study  the  location  of  highly  pro- 
ductive wells  near  faults  suggests  the  desirability  of  drilling  in  the  south- 
west corner  of  Sec.  7,  T.  18  S.,  R.  15  W.,  and  in  the  adjoining  territory  in 
Sees.  12  and  13,  T.  18  S.,  R.  16  W.  The  field  may  probably  also  be  ex- 
tended in  the  SE%  SE^i  Sec.  32,  T.  17  S.,  R.  15  W.,  and  there  seems  to  be 
no  indication  that  the  producing  territory  will  not  also  include  parts  at 
least  of  the  SW%  Sec.  33,  T.  17  S.,  R.  15  W.,  and  of  the  NW&,  NW%,  Sec. 
4,  T.  18  S.,  R.  15  W.  A  well  in  the  NW*4  Sec.  7,  T.  18  S.,  R.  15  W.,  should 
yield  either  oil  or  gas,  particularly  in  the  eastern  part  of  the  quarter  sec- 
tion. The  same  is  true  of  Sections  18  and  19  in  the  same  township. 

A  number  of  test  wells  should  be  drilled  west  of  the  gas-bearing  area, 
for  oil-bearing  beds  may  possibly  border  the  gas-bearing  beds  on  the  west 
and  south  as  they  do  on  the  north  and  east.  Suggested  locations  for  test 
wells  are  the  northeast  corner  of  Sec.  2,  T.  18  S.,  R.  16  W.,  the  center  of 
the  N%  Sec.  2,  T.  18  S.,  R.  16  W.,  and  the  center  of  the  N%  Sec.  12,  T.  18 
S.,  R.  16  W. 

The  extension  of  the  field  to  the  south  of  its  present  limits  is  to  be 
expected,  and  determined  prospecting  to  discover  a  northward  extension  is 
also  justified  by  the  peculiar  type  of  structure.  Operators  should  not  accept 
a  single  dry  hole  as  limiting  the  field  in  these  directions.  The  producing 
territory  at  the  present  north  margin  of  the  field  can  probably  be  extended 
westward. 

Possibility  of  Similar   Fields   Elsewhere    in   Southern   Arkansas. 

Parallel  belts  of  faults  separated  by  areas  almost  unfaulted  may  occur 
in  southern  Arkansas  as  they  do  elsewhere  in  the  mid-continent  region, 
notably  in  northern  Oklahoma  and  southern  Kansas.  If  such  a  belt  exists 
within  a  few  miles  of  El  Dorado  the  other  favorable  conditions  that  com- 
bined to  produce  the  El  Dorado  pool  probably  also  exist  there  and  a  field 
much  like  the  Ei  Dorado  field  may  be  developed.  Because  of  this  probability 
the  following  suggestions  are  made. 

1.  If  gas  in  volume  is  encountered  in  a  wildcat  well  the   search  for 
oil  should  be  continued  by  wells  drilled  east,  northeast,  or  southeast  of  the 
gasser. 

2.  If  oil  is  encountered  in  a  wildcat  well  the  extension  of  the  oil-yield- 
ing area  should  be  sought  by  other  wells   drilled  either  north  or  south  of 
the  discovery  well. 

3.  Gas  pressure  should  be  conserved   by   shutting  in  gas  wells.     The 
maintenance  of  the  high  gas  pressure  will  help  to  promote  greater  extrac- 
tion of  oil  and  to  prevent  water  trouble. 


76  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

The  chances  for  finding  new  fields  are  not  limited  to  zones  of  faulting, 
for  there  are  probably  anticlines  in  southern  Arkansas  fully  as  strongly 
developed  as  those  on  which  the  Homer  and  Bellevue  fields  of  Louisiana 
are  located.  Even  if  some  of  the  conclusions  here  presented  may  be  ques- 
tioned, other  oil  fields  will  no  doubt  sooner  or  later  be  discovered  in  southern 
Arkansas,  for  in  view  of  the  showings  of  oil  obtained  in  widely  scattered 
wells  in  this  broad  region  it  would  be  unreasonable  to  believe  that  there  is 
only  one  place  in  it  where  the  conditions  are  favorable  to  the  formation  of 
an  oil  pool. 

Description   of  the   Producing    Bed: 

The  Nacatoch  sand  in  the  El  Dorado  field  is  about  180  to  190  feet  thick. 
The  upper  part  is  principally  sand,  but  the  formation  also  includes  shaly 
sandstone  and  streaks  of  gumbo  and  shale.  The  lower  part  varies  from 
slightly  calcareous  shale  to  hard  limestone,  although  it  generally  contains 
some  thin  sandy  layers. 

The  top  of  the  sand  is  commonly  marked  by  hard  streaks  called  "rock" 
'by  the  drillers.  At  some  places  these  hard  streaks  are  absent,  and  drillers 
who  depended  on  them  to  indicate  the  top  of  the  pay  sand  drilled  deep  into 
the  sand  before  they  realized  that  they  had  reached  the  oil-bearing  bed.  In 
fact,  the  drillers  of  the  Busey  well,  commonly  considered  the  discovery  well 
of  the  field,  drilled  through  the  bed  that  yields  most  of  the  oil  produced 
from  the  surrounding  wells  without  recognizing  it  and  obtained  oil  from 
a  lower  pay  streak  in  the  sand. 

There  are  at  least  three  pay  streaks  in  the  upper  part  of  the  Nacatoch. 
No  one  of  these  three  streaks  appears  to  extend  through  the  field  but  the 
middle  one,  which  is  about  forty  feet  below  the  top  of  the  sand,  is  nearly 
continuous  and  yields  most  of  the  oil.  Producing  beds  both  higher  and 
lower  than  the  middle  one  have  made  good  wells,  but  these  other  producing 
beds  appear  to  be  very  patchy  or  perhaps  they  have  not  been  adequately 
tested,  for  comparatively  few  drew  oil  from  them.  The  gas  well  drilled  by 
the  Constantine  Refining  Company,  which  was  the  real  discovery  well  of 
the  field,  obtained  its  gas  from  a  bed  that  lies  about  forty  feet  below  the 
bed  which  is  yielding  oil  in  wells  to  the  east. 

In  all  the  pay  streaks  oil  seems  to  be  present  only  in  the  topmost  few 
feet  of  the  sand  and  is  everywhere  underlain  by  salt  water.  Salt  water  is 
also  closely  associated  with  the  gas  in  the  gas-yielding  part  of  the  field. 
Unless  a  well  is  completed  with  the  utmost  care  this  water  flows  from  it 
with  the  oil  and  gas  from  the  day  it  is  completed  until  water  flooding  causes 
its  abandonment.  This  water  is  much  more  difficult  to  combat  than  the 
water  in  most  pools,  because  there  is  no  such  thing  in  this  field  as  "edge 
water,"  which  is  restricted  to  the  margins  of  the  producing  area.  So  far 
as  salt  water  is  concerned  this  field  may  be  said  to  be  all  "edge"  and  each 
well  is  a  problem  in  itself. 

There  is  no  evidence  that  the  Nacatoch  is  either  thinner  or  more  shaly 
near  the  edges  of  the  field  than  elsewhere.  It  is  undoubtedly  much  more 
shaly  in  some  places  than  in  others,  but  no  relation  between  the  yield  of 
oil  and  the  percentage  of  clean  sand  could  be  determined. 

Methods  Used   in  Constructing  the   Map: 

The  records  of  wells  drilled  with  rotary  tools  are  notoriously  poor  and 
afford  very  unreliable  correlations.  In  the  El  Dorado  field  comparisons  and 
correlations  are  particularly  hard  to  make,  because  the  top  of  the  Nacatoch 
sand  varies  so  little  in  evelation  throughout  the  field  and  because  no  sin- 
gle bed  can  be  easily  and  certainly  recognized  everywhere.  The  results  pre- 
sented on  the  map  are  admittedly  open  to  challenge,  but  they  represent 
very  careful  and  painstaking  work — the  best  that  can  be  done  with  the 
data  available. 

The  correlation  of  the  beds  struck  in  different  wells  was  first  attempted 
solely  by  noting  the  relative  positions  of  the  beds  of  sandstone,  limestone 
chalk,  and  gypsum  recorded  by  the  drillers.  The  results  of  these  correla- 
tions were  not  satisfactory.  Next,  the  "rocks"  recorded  by  the  drillers  were 
colored  distinctively  on  the  plotted  well  logs  and  were  found  to  furnish  a 
good  tie  between  many  of  the  wells.  However,  to  make  satisfactory  corre- 
lations it  was  found  necesary  to  assign  characteristic  symbols  or  colors  to 
every  term  employed  by  the  drillers.  The  record  of  hardness  was  heloful. 
"Boulders"  were  in  places  distinctive.  Some  of  the  "pack  sands"  could  be 
correlated  '  between  two  or  more  wells.  Shale  and  gumbo  were  distin- 


EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 77 

guished,  and  although  the  usage  of  the  drillers  was  not  uniform  their  use 
of  these  terms  furnished  a  valuable  clue  for  many  areas. 

The  work  thus  done  permitted  the  recognition  of  small  faults  shown  on 
the  map.  These  faults  would  have  been  indicated  by  the  evidence  afforded 
by  the  oil  sands,  but  this  indication  had  to  be  confirmed  in  the  upper  part 
of  the  section.  In  a  record  of  a  well  drilled  across  a  normal  fault  a  part  of 
the  stratigraphic  section  is  missing,  and,  conversely,  in  a  record  of  one 
drilled  across  a  reverse  fault  a  part  of  the  section  is  repeated.  In  parts  of 
the  map  that  are  based  on  comparatively  few  well  records  the  structure 
appears  to  be  much  smoother  and  simpler  than  it  is  elsewhere,  but  if  more 
records  had  been  available  these  apparently  simple  areas  would  no  doubt 
prove  to  be  much  more  complex. 

Character  of  the  Oil: 

Detailed  analyses  of  the  oil  from  the  El  Dorado  field,  published  by  the 
United  States  Bureau  of  Mines  November,  1921,  show  that  its  gravity  is 
about  34.2  Baume,  and  it  contains  about  30  per  cent  of  gasoline  and  naphtha 
and  13  per  cent  of  kerosene,  the  remainder  being  gas  oil  and  lubricating  oil. 


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EL  DORADO.  ARK..  OIL  AND  GAS  FIELD 


Geology  of  the  El  Dorado  Field  and  Some 
Mistakes  in  Drilling  Methods 

(Prepared  by  the  TJ.  S.  Geological  Survey) 

Of  the  many  wells  that  have  been  drilled  in  south-central  Arkansas  for 
oil,  several  apparently  stopped  short  of  the  sand  that  yields  the  oil  at  El  Do- 
rado, in  Union  County,  and  the  greater  number  did  not  reach  the  sand 
that  yields  oil  in  the  Haynesville  field,  in  Claiborne  Parish,  La.,  is  the 
opinion  of  the  United  States  Geological  Survey,  Department  of  the  Inte- 
rior. Furthermore,  practically  all  drilling  has  been  done  with  rotary  tools, 
a  method  which  not  only  yields  inaccurate  records  of  the  formation  pene- 
trated but  which  also  requeutly  prevents  the  recognition  and  testing  of 
oil  sands  that  may  be  drilled  through. 

Several  sands  in  northern  Louisiana,  below  the  Nacatoch,  have  pro- 
duced much  more  oil  than  the  Nacatoch,  and  in  some  of  the  fields  the  Naca- 
toch is  practically  barren,  in  spite  of  the  immense  volume  of  oil  in  the  un- 
derlying sands.  The  deepest  formation  in  this  region  that  now  seems 
worth  testing  is  estimated  to  lie  4,000  or  5,000  feet  below  the  surface  and 
may  be  below  profitable  drilling  depth.  This  formation  is  the  Trinity,  which 
in  Pike  and  Sevier  counties,  Arkansas,  contains  asphalt  deposits  that  rep- 
resent the  meager  remains  of  what  were  once  rather  large  bodies  of  oil. 

Although  the  character  of  the  formations  in  southern  Arkansas  may 
require  the  use  of  the  rotary  drill,  operators  should  realize  its  shortcomings 
and  employ  methods  that  will  insure,  so  far  as  possible,  detection  of  show- 
ings of  oil  and  gas.  Cores  should  be  cut  from  all  beds  penetrated  that 
yield  showings,  and  particularly  from  a  sand  near  the  base  of  the  Midway 
formation  and  from  sands  in  the  Nacatoch,  Marlbrook,  Brownstown,  Blos- 
som, Eagle  Ford,  Woodbine,  and  Trinity  formations,  whether  or  not  oil 
showings  are  observed  in  the  sludge. 

The  ages,  relative  positions,  and  thicknesses  of  the  formations  encoun- 
tered in  drilling  in  south-central  Arkansas  must  be  determined  if  the  search 
for  oil  is  to  be  carried  out  effectively  and  economically.  These  determina- 
tions are  difficult  because  of  the  similarity  of  the  beds  of  the  several  for- 
mations, and  can  be  made  precise  only  with  the  aid  of  fossils.  The  ap- 
proximate boundaries  of  the  larger  units,  however,  may  be  determined  from 
the  character  of  the  beds  as  shown  by  well  records.  The  following  descrip- 
tions of  formations  encountered  by  drillers  in  Union  County,  Arkansas,  are 
the  result  of  a  detailed  study  of  many  well  records  by  W.  W.  Rubey,  of  the 
U.  S.  Geological  Survey,  Department  of  the  Interior.  Inaccuracies  in  the 
well  records  may  have  caused  like  inaccuracies  in  the  interpretation  of  the 
stratigraphy. 

Probably  all  the  rocks  that  cover  the  surface  of  Union  County  belong 
to  the  Claiborne  group  of  the  Eocene  series  of  the  Tertiary  system,  which 
in  this  general  region  is  divided  into  two  formations,  the  Yegua  above  and 
the  St.  Maurice  below. 

Yegua   (?)    Formation: 

Recent  determinations  of  fossil  plants  by  E.  W.  Berry  indicate  that  the 
Yegua  (?)  formation  is  probably  present  in  Union  County,  and  that  it  com- 
prises the  surface  beds  over  most  of  the  county.  The  beds  that  are  prob- 
ably to  be  assigned  to  the  Yegua  ("Cockfield")  formation  are  recorded  in 
well  records  as  alternating  layers  of  sand  and  gumbo,  some  shale  and  cal- 
careous material  ("boulders"  and  "rocks"),  and  a  little  lignite.  They  may 
"be  distinguished  from  the  underlying  beds  by  their  dominant  sandiness. 
These  beds  probably  attain  a  maximum  of  slightly  more  than  450  feet  in 
the  southeastern  part  of  the  county. 

St.   Maurice   Formation: 

The  strata  in  this  area  which  are  here  identified  as  the  St.  Maurice  for- 
mation are  commonly  recorded  in  drillers'  logs  as  layers  of  shale  and 
gumbo  with  many  "boulders"  and  "rocks"  and  some  sandy  material.  The 
St.  Maurice  is  much  freer  from  sand  than  the  formations  above  and  below 
it.  It  probably  ranges  in  thickness  from  90  feet  in  the  northwest  corner  of 
the  county  to  about  200  feet  in  the  southeastern  part'  . 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


Wilcox   Formation: 

The  Wilcox  formation  is  generally  shown  in  logs  as  thick  alternating 
layers  of  sand,  sandy  gumbo,  and  shale,  with  some  zones  marked  by  "rocks" 
and  "boulders,"  although  subordinate  amounts  of  gravel  and  lignite  are  oc- 
casionally noted.  This  formation  can  be  recognized  by  an  upper  sandy 
group  and  a  lower  shaly  group  which  contain  less  sand.  Its  thickness 
averages  about  600  feet  throughout  Union  County,  but  increases  slightly 
toward  the  east. 

Formations  similar  in  composition  to  the  Wilcox  have  yielded  small 
quantities  of  oil  in  Louisiana  and  Texas,  and  the  expectation  that  some  oil 
may  be  obtained  from  this  formation  in  restricted  areas  is  not  unreasonable. 
A  careful  watch  should  therefore  be  kept  for  indications  of  oil  or  gas 
while  wells  are  penetrating  these  beds. 

Midway  Formation: 

The  beds  referred  to  as  the  Midway  formation  are  recorded  by  the 
drillers  as  "boulders,"  "rocks,"  and  layers  of  sand,  gumbo,  and  shale,  with 
more  or  less  chalk,  limestone,  and  gypsum.  Recent  microscopic  studies  of 
cuttings  from  wells  in  the  El  Dorado  field  by  James  Gilluly,  of  the  U.  S. 
Geological  Survey,  have  shown  these  beds  to  include  some  lignite.  This 
occurrence  of  carbonaceous  material  in  .the  Midway,  although  by  no  means 
widespread,  is  nevertheless  not  unusual.  This  formation  is  characterized 
throughout  by  its  relative  hardness. 

The  greatest  known  thickness  of  the  Midway  at  its  outcrop  is  about  260 
feet*  but  this  measurement  was  taken  near  the  shore  line  of  the  embayment 
in  which  the  formation  was  deposited.  The  character  of  the  strata  pene- 
trated indicates  that  the  formation  probably  attains  a  maximum  thickness 
of  slightly  more  than  500  feet  in  Union  County. 

Many  wells  drilled  in  south-central  Arkansas  have  obtained  showings 
of  oil  or  gas  or  flows  of  water  in  a  sandy  bed  near  the  base  of  this  forma- 
tion. At  only  a  few  wells,  however,  have  tests  been  made  to  ascertain  the 
true  value  of  these  showings.  Especially  in  the  El  Dorado  field  has  this 
bed  remained  untested. 

Arkadelphia  Clay: 

The  Arkadelphia  clay  of  the  Upper  Cretaceous  or  Gulf  series  is  in  gen- 
eral easily  recognized  by  its  thickness  and  its  freedom  from  sand.  The 
strata  recorded  are  mainly  shale  and  gumbo,  which  are  generally  accom- 
panied by  many  layers  of  "boulders,"'  "rocks."  chalk,  limestone,  and  gyp- 
sum, and  in  a  few  wells  layers  of  sandy  shale.  A  very  noticeable  group  of 
chalky  or  calcareous  beds  makes  up  the  lower  175  or  200  feet  of  the  Arka- 
delphia. The  thickness  of  this  formation  averages  about  550  feet  in  the 
western  part  of  Union  County  and  increases  eastward,  possibly  to  as  much 
as  600  feet  near  the  eastern  boundary. 

Nacatoch  Sand: 

The  drillers'  logs  record  the  Nacatoch  sand  as  beds  of  hard  sand,  shale, 
and  limestone  with  may  layers  of  "rocks,"  ''boulders,"  and  "pyrite"  and 
some  gumbo  and  chalky  material.  The  upper  part  is  commonly  hard  and 
sandy;  the  lower  varies  from  slightly  calcareous  shale  to  hard  limestone, 
although  it  usually  includes  thin  sandy  layers.  The  thickness  ranges  from 
150  to  200  feet. 

The  Nacatoch  has  been  identified  by  its  fossils  as  the  producing  sand 
at  El  Dorado. t  The  oil  there  is  obtained  from  three  or  four  discontinuous 
layers  of  sandstone  in  the  upper  fifty  feet  of  the  formation. 

Marlbrook  Marl: 

The  Marlbrook  marl  is  recorded  as  shale,  chalk,  "boulders,"  limestone, 
and  lesser  amounts  of  gumbo,  "rocks,"  and  "pyrite,"  and  some  sandy  shale. 
This  formation  consists  typically  of  shale  and  varying  amounts  of  calca- 
reous material.  It  ranges  in  thickness  from  about  300  to  nearly  350  feet. 


ft/.  5".  GeoL  Survey  Press  Notice:  Oil  from  the  Nacatoch  Sand,  El  Dorado, 
Ark.,  Feb.  7,  1922. 

*Kennedy,  William.  A  section  from  Terrell,  Kaufman  County,  to  Sabine  Pass 
on  the  Gulf  of  Mexico:  Texas  Geol.  Survey,  Third  Annual  Report,  p.  49,  1892. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  81 

A  group  of  sandy  shales  between  400  and  500  feet  below  the  top  of  the 
Xacatoch  usually  yields  water  wherever  it  is  penetrated.  The  beds  at  this 
horizon  may  contain  oil  or  gas  where  the  structure  is  favorable. 

Annona  Tongue  of  the   Austin   Chalk    (?): 

Fossils  obtained  from  one  of  the  wellst  indicate  the  Marlbrook  age  of 
strata  at  least  250  feet  below  the  base  of  the  Nacatoch  sand,  and  as  no 
marked  change  in  the  character  of  the  sediments  down  to  the  Brownstown 
marl  is  recorded,  the  Annona  tongue  of  Austin  chalk  may  be  absent  here. 
However,  as  this  tongue,  in  its  area  of  outcrop,  varies  from  typical  chalks 
to  calcareous  clays,  it  is  probably  present  in  Union  County,  but  because  of 
this  lithologic  variation  it  may  not  be  easily  distinguished  from  the  over- 
lying Marlbrook  marl.  The  boundary  between  the  Marlbrook  marl  and  the 
Annona  tongue  of  the  Austin  is  provisionally  drawn  at  the  upper  surface 
of  a  persistent  limy  or  chalky  series.  As  thus  identified  the  Annona  tongue 
in  Union  County  consists  of  strata  recorded  in  logs  as  limy  shale,  gypsum, 
and  gumbo,  with  some  "rocks,"  sandy  shale,  or  chalk;  its  thickness  ranges 
from  60  to  100  feet  . 

Brownstown   Marl: 

The  strata  referred  to  the  Brownstown  marl  are  dominantly  calcareous 
sandy  shales.  They  are  usually  called  sandy  shale,  hard  shale,  "rock," 
sand,  and  gumbo  in  drillers'  logs.  Subordinate  amounts  of  lime  stone, 
"boulders,"  "pyrite,"  gypsum,  and  chalk  are  frequently  noted.  The  thick- 
ness of  the  Brownstown  ranges  from  about  200  to  nearly  300  feet  and  ap- 
parently increases  westward. 

The  formation  is  unique  among  those  penetrated  in  that  its  thickness 
seems  to  decrease  eastward  across  Union  County.  This  fact  is  doubtless 
associated  with  a  marked  increase  in  sandiness  of  the  Brownstown  from 
its  outcrop  in  Hempstead  County  southeastward  through  Union  County. 
Any  conclusions  as  to  the  cause  of  these  changes  would  be  unwarranted  if 
based  entirely  on  evidence  furnished  by  records  of  rotary-drilled  wells,  but 
the  presence  of  these  sandy  layers  may  well  justify  a  thorough  test  of  this 
formation. 

Blossom    (?)    Sand: 

A  group  of  beds  below  the  Brownstown  marl,  consisting  of  about  65  feet 
of  sandstone,  shale,  and  some  calcareous  layers,  is  probably  to  be  correlated 
with  the  upper  part  of  the  Bingen  formation  of  southwestern  Arkansas  and 
is  therefore  tentatively  referred  to  as  the  Blossom  sand.  The  Bingen  for- 
mation is  considered  by  L.  W.  Stephenson  "as  the  probable  near-shore  equiv 
alent  of  the  Blossom  sand,  the  Eagle  Ford  clay,  and  part  of  the  Woodbine 
sand,  but  these  formations  are  probably  represented  in  part  by  unconfor- 
mities within  the  Bingen  and  at  its  base.  Indeed,  it  is  possible  that  the 
Woodbine  sand  is  entirely  represented  by  the  unconformity  at  the  base  of 
the  Bingen."  Sandy  layers  in  the  upper  part  of  the  Blossom  (?)  sand  com- 
monly carry  water  and  are  thought  to  correspond  to  the  oil  sand  or  sands 
in  the  Haynesville  field,  in  Louisiana,  although  the  formations  there  have 
not  been  positively  identified.  The  Blossom  (?)  sand  lies  from  800  to  850 
feet  below  the  top  of  the  Nacatoch  sand  over  most  of  Union  County  and 
probably  about  810  to  830  feet  in  the  productive  part  of  the  El  Dorado  field. 

Eagle   Ford   (?)   Clay: 

The  several  hundred  feet  of  calcareous  or  limy  shales  below  the 
Blossom  (?)  sand  that  have  been  penetrated  in  Union  County  probably  be- 
long to  the  Eagle  Ford  ( ?)  clay  of  Upper  Cretaceous  age.  In  the  logs  of 
some  wells  in  and  near  Union  County  a  few  red  layers  are  recorded  from 
these  shales  (see  the  accompanying  cross  section),  and  in  parts  of  the 
Bingen  formation  of  southwestern  Arkansas  that  are  presumably  to  be  corre- 
lated with  the  true  Eagle  Ford  clay  much  reddish  material  has  been  noted, 
both  at  the  outcrop*  and  in  wells. t 


*Miscr.  H.  D..  and  Purdue.  A.  H..  Grarcl  Deposits  of  the  Caddo  Gap  and 
PC  Queen  Quadrangles,  Ark.:  U.  S.  Gcol.  Survey  Bull.  690,  />/>.  22-24,  1919. 

IMiser,  H.  D.,  and  Purdue,  A.  H.,  Asphalt  Deposits  and  Oil  Conditions  in 
Southwestern  Ark.:  U.  S.  Geol.  Survey  Bull.  691,  Pt>.  282-291,  IQIQ. 

tL'.  5.  Geol.  Survey  Press  Notice:  Oil  from  the  Nacatoch  Sand,  El  Doradc. 
Ark.,  Feb.  7,  1922. 


82  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

The  principal  oil  sands  of  the  Caddo  and  DeSoto-Red  River  districts,  in 
Louisiana  (which  are  commonly  but  erroneously  called  the  Woodbine  sand), 
are  probably  of  Eagle  Ford  age.fl  The  horizon  of  these  oil-bearing  strata 
in  Louisiana  is  estimated  to  lie  500  feet  more  or  less,  below  the  top  of  the 
Blossom  (?)  sand  in  Union  County,  Ark.,  and  from  about  1,300  to  1.400  feet 
below  the  upper  surface  of  the  Nacatoch.  So  far  as  known,  this  horizon 
has  not  been  reached  in  Union  County. 

RECORD  OF  DEEP  WELL  NEAR  EL  DORADO 

Detailed  information  regarding  the  nature  of  the  beds  penetrated  may 
be  obtained  from  the  following  record  of  one  of  the  deepest  wells  in  Union 
County,  Hammond  well  No.  1  of  Cooper  &  Henderson  Oil  Company,  in  SEV4 
SW%,  Sec.  19,  T.  17  S..  R.  15W.: 

(Elevation  above  sea  level  about  204  feet.  Geologic  correlations  by 
U.  S.  Geological  Survey.  All  tormational  boundaries  are  fixed  tentatively 
except  that  between  the  Arkadelphia  and.  Nacatoch.) 

Material  Thickness        Depth 

Eocene  series: 
Claiborne  group: 

Yegua  (?)  formation: 

Surface    sand 30  30 

Sand    20  50 

Gumbo    11  61 

Packed  sand 6  67 

Rock 3  70 

Packed  sand  40  110 

Hard  sand 45  155 

Rock    2  157 

Hard  sand 20  177 

Gumbo;    set  12%-inch  casing 4  181 

Gumbo    6  187 

Sand  and  boulders... , 6  193 

Packed  sand   and  boulders : 20  213 

Gumbo    25  238 

Rock   and   sand 2  240 

Packed  sand  10  259 

Sandrock 5  2o5 

Sand  and  boulders 3  258 

Sand    boulders    and    gumbo 100  358 

St.  Maurice  formation  (position  of  contact  doubtful; 

lies    above   in   the    100    feet   of   sand,    boulders    and 

gumbo) : 

Sand  and  boulders 18  376 

Rock    2  378 

Packed    sand    9....  387 

Rock 3  390 

Gumbo    10  400 

Sand  and  gumbo 20  420 

Gumbo    22  442 

462 
504 

518  : 

536 

679    . 

702       . 

708. 

751 

805 
813 


Wilcox  formation: 
Boulders    
Boulders    
Sand  and  boulders  
Packed    sand    

20 

I   14 
18 
36 

107 

Sand  and  boulders  : 
Gumbo    
Sand  and  boulders  
Gumbo    
Gumbo    
Gumbo  and  boulders  

23 
6 
43 
26 
28 
8 

_  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

Rock    4  817 

Gumbo 7  824 

Gumbo    41  865 

Rock    3  868 

Gumbo  and  boulders 8  876 

Gumbo  and  -boulders 30  906 

Gumbo    5  911 

Gumbo  and  boulders 42  953 

Packed  sand  10  963 

Broken    sandrock 6  969 

Gumbo    20  .  989 

Sand 16  1,005 

Sandrock 19  1,024 

Midway  formation: 

Hard  sand  6  1,030 

Gumbo    6  1.036 

Gummy  shale ,  20  1,056 

Sand  and  boulders 27  1,083 

Gumbo    15  1,098 

Sand   and.  sandrock 7  1,105 

Broken  formation 23  1,128 

Broken  formation  13  1,141 

Sandy  gumbo  : 15  1,156 

Gumbo    71  1,227 

Shale  : 12  1,239 

Sand  and  boulders.. 11  1,250 

Gumbo    20  1,270 

Gumbo    14  1,284 

Rock 1  1,285 

Rock 2  1,287 

Gumbo    14  1,301 

Lignite 5  1,306 

Gumbo    14  1 ,320 

Gumbo    20  1,340 

Rock    1  1,341 

Sand 12  1,353 

Sand    and    boulders 8  1,361 

Gypsum    31  1,392 

Gumbo    8  1,400 

Gumbo    : 86  1,486 

Gumbo    25  1,511 

Rock  ' 3  1,514 

Rock    3  1,517 

Upper  Cretaceous  or  Gulf  series: 

Arkadelphia  Clay: 

Gumbo    10  1,527 

Gumbo    23  1,550 

Hard   shale 5  1,555 

Gumbo    8  1,563 

Gumbo 1 2  1.575 

Gumbo    20  1,595 

Shale „. 5  1,600 

Gumbo    30  1,630 

Gummy  shale  4  1,634 

Gummy  shale  60  1,694 

Gumbo    52  1,746 

Shale  and  gumbo 65  1,811 

Shale   and   boulders 10  1,821 

Shale  - 23  1,844 

Gummy  shale  18  1,862 

Shale  and  gumbo 30  1,892 

Gumbo    27  1,919 

Gypsum    10  1.929 

Hard   shale : 20  1.949 

Gumbo    - .  27  1.976 

Gumbo  and   shale 44  2.020 

Hard  shale  and  gumbo;    set  S^-inch  casing 25  2,045 

Gumbo : 5  2,050 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


Gumbo   and  shale 

Gumbo  and  shale 

Shale  and  gumbo 
Nacatoch  sand: 

Hard  lime  and  shale 

Gumbo 

broken  rock 

Sand    ...................................  -• 

Sand 

Broken  rock 

Sand    .....  : 

Sand 

Rock 

Sand 

Sand 

Shale   and   boulders 

Gumbo 

Gummy    shale 

Shale  and  gumbo 

Gummy  shale  ............................  . 

Shale  and  lime  ..... 
Marlbrook  marl: 

Shale  and   boulders 

Gummy  shale 

Shale   and   boulders 

Hard  shale 

Hard  shale 

Salt-water  sand 

Rock 
.Sandrock 

Sandrock 

Sandy  shale 

Gummy  shale 

Rock 

Gummy  shale 

Shale 

*Sandy  shale 
.    Hard  shale   .........................  ... 

Rock 

Gumbo 

Gumbo 

Gumbo 

Gumbo    ...... 

Hard  shale   ............................. 

Annona  tongue  of  Austin  chalk 

Broken  sandrock 

Broken    sandrock 

Hard   shale 

Gumbo 

Gumbo 

Hard  sand 

nock 

Gumbo 

Lime    and    shale 

Rock 

Lime  and  shale 
Brownstown  marl: 

Gumbo 

Rock 

Gumbo 

Gumbo 

Hard    sandy    shale 

Gumbo 

Gumbo 

Sand,   showing  salt  water 

Gumbo 

Hard   gummy    shale 

Rock 


24 
.......  48 

26 
14 

45 
41 
14 
95 
15 


2,082 
2,J96 
2,111 

2,117 
2,137 
2,140 
2,146 
2,148 
2,150 
2,156 
2,160 
2,164 
2,166 
2,170 
2,184 
2,189 
2,213 
2,261 
2,287 
2,301 

2,346 
2,387 
2,401 
2,496 
2,511 
2,519 
2,521 
2,523 
2,528 
2,530 
2,535 
2,537 
2,544 
2,548 
2,552 
2,565 
2,567 
2,579 
2,594 
2,604 
2,624 
2,629 

2,633 
2,637 
2,650 
2,653 
2,662 
2,665 
2,669 
2,675 
2,700 
2,702 
2,727 

2,734 
2,740 
2,741 
2,755 
2,765 
2,770 
2,774 
2,780 
2,792 
2,814 
2,822 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD  85 

Rock    ..  .     »  2,825 

Rock    5  2,830 

Hard    sandy    shale 26  2,856 

Hard    sandy    shale 21  2,877 

Gumbo    5  2,882 

Hard  shale   3  2,885 

Hard   shale   9  2,894 

Rock  1  2,895 

Rock    '. 3  2,898 

Shale    3  2,901 

Shale  and  gumbo 5  2,906 

Hard    sandy    chalk 4  2,910 

Sandy  chalk  ...  14  2,924 

Hard   shale  -'.-» ...  15  2,939 

Blossom  (?)  sand: 

Sand    2  2,941 

Sand 14  2,955 

Rock   3  2,958 

Sand 2  2,960 

Sandrock   .1 2  2,962 

Gumbo    20  2,982 

Sandy  shale   8  2,990 

Shale  and  boulders 1  2,991 

Rock   1  2,992 

Sand 6  2,998 

Sand  and  gravel 7  3,005 

Eagle  Ford  (?)  clay: 

Gumbo 14  3,019 

Gummy  shale 7  3,026 

Gumbo    22  3,048 

Gummy  shale  ! 9  3,057 

Broken  limerock  28  3,085 

Shale    7  3,092 

Broken   limerock   and    shale 22  3,114 

Shale    6  3,120 

Broken  limerock  20  3,140 

Shale    6  3,146 

Broken  limerock  and  shale 17  3,163 

Broken  lime  and  shale 37  3.200 

Geologic   Structure   in  the   Region: 

The  accompanying  cross  section,  from  the  vicinity  of  Centerpoint, 
Howard  County,  Ark.,  in  the  Caddo  Gap  quadrangle,  to  a  point  about  ten 
miles  east  of  El  Dorado,  Union  County,  shows  the  general  structural  con- 
ditions in  south  central  Arkansas.  The  diminishing  slope  and  the  general 
increase  of  thickness  of  the  formations  as  the  center  of  the  embayment 
is  approached  is  readily  apparent. 

The  elevation  of  the  surface  as  shown  is  based  on  a  partial  revision  of 
a  map  previously  published  by  the  Survey*,  and  is  included  in  this  dia- 
gram to  show  the  relation  of  outcrops  to  formation  below  the  surface  and 
the  depth  of  the  oil  and  gas  bearing  sands.  Topographic  details  near  the 
wells  are  necessarily  obscured  because  of  the  exaggerated  width  of  the 
graphic  logs.  The  records  of  the  Nashville,  Hope,  and  Bodcaw  wells  with 
correlations?  and  the  outcrops  of  the  formations}!  were  taken  from  pub- 
lished reports. 


*  Harris,  G.  D.,  Oil  and  Gas  in  Louisiana:  V.  S.  Gcol.  Surrey  Bulletin  429, 
pi.  12.  1910. 

*A  small  fossil  obtained  from  this  depth  indicates  that  these  beds  are  no 
older  than  the  Marlfronk  marl. — U.  S.  Geol.  Survev  Press  Notice:  Oil  from 
the  Nacatoch  Sand,  El  Dorado.  Ark.,  Feb.  ~,  1922. 


M-;  EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 

The  strata  recorded  in  a  number  of  the  available  logs  of  wells  drilled 
in  and  near  Union  County  were  also  correlated  and  the  results  are  given  in 
the  descriptions  of  the  formations.  Maps  showing  the  structure  of  the 
Xacatoch  and  other  formations  in  south  central  Arkansas  have  been  pre- 
pared bv  Veatch§.  A  general  structural  contour  map  of  Union  County 
has  not  been  made,  as  a  sufficient  number  of  well  logs  for  that  purpose  has. 
not  been  obtained,  but  the  position  relative  to  sea  level  of  the  upper  sur- 
face of  the  Nacatoch  sand  and  other  interesting  features  of  the  wells  studied 
are  given  in  the  following  tabulation. 


+Miser,  H.  D.,  and  Purdue,  A.  H.,  Asfhalt  Deposits  and  Oil  Conditions  in 

Southwestern  Arkansas:  U.  S.  Gcol.  Surrey  Bulletin  6yi,  />/>.  2X2-2^2.  />/.  .?j,  /y/v. 

^Harris,  G.  D.,  Oil  and  Gas  in  Louisiana:    U.  S.  Gcol.  Survey  Bulletin  .}_>,. 

/>/.     12;    1910. 

§]~eatch,  A.  C.,  Geology  and   Underground    H'atcr  Resources  of  Xortlieni 
Louisiana  and  Southern  Arkansas:    U.  S.  Gcol.  Surrey  Prof.  Paper  46.  mnf). 


PART  III 

New  Wells   Show  Extension 
of  El  Dorado  Field 

On  the  eve  of  going  to  press  with  the  final  forms  of  this  report,  infor- 
mation was  received  by  the  department  of  the  bringing  in  of  several  new 
wells,  indicating  a  considerable  extension  of  the  El  Dorado  Field,  espe- 
cially in  a  north  and  east  direction.  Mr.  J.  A.  Brake,  State  Oil  and  Gas 
Inspector,  El  Dorado,  Ark.,  has  kindly  furnished  the  department  with  logs 
and  photographs  of  these  new  wells,  and  this  information  is  supplemented 
to  that  which  had  already  been  prepared  by  the  authors  of  this  report,  with 
the  explanation  that  there  was  no  opportunity  for  these  authors  to  make 
comment  upon  the  new  wells  or  the  bearing  of  these  important  discoveries 
upon  future  developments  in  the  field.  Mr.  Brake  says:  "The  new  wells 
are  a  revelation.  The  log  of  the  deep  sand,  which  shows  the  new  field,  and 
the  log  of  the  north  field,  which  shows  still  another  formation,  I  think  art- 
better  than  any  we  have  yet  found." 

East  Field   Four  Miles   East  of  El  Dorado. 

Six  big  gas  wells  have  been  brought  in  in  the  East  Field,  two  of  them 
making  45,000,000  cubic  feet  each  with  a  rock  pressure  of  1.050  pounds.  The 
other  four  wells  are  two  and  one-half  miles  farther  north  and  they  are  mak- 
ing 20,000.000  cubic  feet  with  a  rock  pressure  of  850  pounds. 

Four  oil  wells  have  been  brought  in  in  this  same  territory,  one  of  them 
making  2,000  barrels  and  still  is  producing  at  The  rate  of  1,200  barrels. 
About  twenty  wells  are  now  being  drilled  in  this  east  field. 

North   Field,   Eight  Miles  North  of  El   Dorado. 

Murphy  No.  1.  in  8-16-13,  shows  a  different  log,  with  much  more  shale, 
than  any  of  the  other  wells,  and  the  sand  is  found  176  feet  higher  than  in 
the  old  field  of  Union  county. 

Log  of   Murphy   No.  1— the  Wild  Well 
Elevation  218  feet.     Location  SYV  Corner  01  NE^i  of  SE*4: 

'I    lo         25.    sand  1163.  gumbo 

183,   sand    and   clay    (set    10-in.  1165.  rock 

casing  116  f.  gumbo 

190,   gumbo  12oo.  gumbo 

I'.".:.,    sand   and   shale  1229.  shale       \ 

288,   gumbo   and    boulders  1232,  rock 

::<HI.   boulders  '  1269,  tough  blue  gumbo 

M33.   sand  and  shale  1309,  gumbo,  blue 

IT.'i,   shale  and  gumbo  1445,  gumbo,   blue 

500,    hard   sand  1490,  gumbo,   black 

608,   gumbo  and  boulders  1581,  gumbo   and   shale,   black 

<i.~jl.   gumbo  lfii.ui.  gumbo,  black 

<!52.   rock  1668,  black    shale   and    boulders 

TIKI,   shale   and   gumbo  1728.  shale    and    boulders 

746.   gumbo   and   boulders  1740.  gumbo,   black 

748,   rock  1760.  shale,   black 

788.    black      shale  1781.  gumbo 

S12.   gumbo   and   boulders.  1795,  gumbo,   black 

895.   shale,    black  1805,  shale 

*J60   gumbo  and   boulders  1841,  gumbo  and   boulders 

!K!6.   packed  sand  and  boulders  1865,  gumbo 

1060.   sticky  shale  1909,  gumbo,   black 

1»<5i.   rock  1960,  gumbo   and   shale 

1062,   rock  1975,  gumbo 

,./o".   snaif.   black  2000,  shale 

1081.    rock  2'!  12.  gumbo 

iti82.   rock  2023.  shale 

I  140.    L -unibo  2024.  sand 

II  "10.   sand,    lignite  and   boulder d 


*8  EL  DORADO.   ARK.,   OIL  AND  GAS  FIELD 


— Photo   by  Taylor 
Burning   Well    by    Day — Murphy    No.   1,   Sec.   8-16-15 


EL,  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


89 


West  Field,  Three  Miles  West  of  El   Dorado. 

On  May  7,  1922,  the  El  Dorado  Natural  Gas  &  Petroleum  Corporation 
brought  in  a  well  on  the  Frazier  lease  in  1-18-16,  making  4,000,000  feet  of 
dry  gas.  After  blowing  for  a  short  time  it  increased  to  45,000,000  and  blew 
off  all  the  fittings  and  went  wild.  The  first  day  after  being  wild  it  com- 
menced making  oil.  This  well  came  from  the  deep,  or  new,  sand  at  2,529 
feet.  The  well  was  successfully  capped  and  closed  in  and  was  at  that  time 
making  50,000,000  feet  of  gas  and  300  barrels  of  oil..  Three  or  four  deep 
test  wells  are  being  drilled  in  the  field  at  this  time. 

Log  of  Frazier  Well 


0 

to 

6, 

surface  sand 

1285 

to 

1330, 

sand 

G 

to 

12, 

sand  and  gravel 

1330 

to 

1340, 

shale                        . 

12 

to 

65, 

clay. 

1340 

to 

1344, 

sand 

65 

to 

160, 

sand  clay 

1344 

to 

1355, 

shale  and  sand 

160 

to 

175, 

sand 

1355 
1375 

to 

to 

1375, 
1408 

gumbo 

ing 

1408 

to 

1412! 

gumbo 

185 

to 

190, 

sand 

1412 

to 

1416, 

rock 

190 

to 

sand  with  clay  and  lime 

1416 

to 

1455, 

sand 

chalk 

1455 

to 

1465, 

shale 

225 

to 

235, 

gumbo 

1465 

to 

1470, 

rock 

235 

to 

265, 

sand 

1470 

to 

1474, 

sand 

265 

to 

285, 

shale 

1474 

to 

1495, 

jipsy  chalk 

285 

to 

300, 

gumbo 

1495 

to 

1498, 

gumbo 

300 

to 

335, 

sand 

1498 

to 

1530, 

rock 

335 

to 

355, 

white  sand 

1530 

to 

1570, 

sand 

355 

to 

380, 

gumbo 

1570 

to 

1580, 

gumbo 

380 

to 

395, 

sand 

1580 

to 

1665, 

shale 

395 

to 

415, 

shale 

1665 

to 

1705, 

gumbo   and  sand 

415 

to 

435, 

gumbo 

1705 

to 

1735, 

rock 

435 

to 

445, 

clay 

1735 

to 

1885, 

sand 

445 

to 

500, 

gumbo 

1885 

to 

1920, 

gumbo 

500 

to 

525, 

sand 

1920 

to 

2005, 

shale 

525 

to 

555, 

gumbo,  brown 

2005 

to 

2025, 

rock 

555 

to 

580, 

rock 

2025 

to 

2035, 

sand 

580 

to 

635, 

gumbo 

2035 

to 

2040, 

gumbo 

•  635 

to 

655, 

sand 

2040 

to 

2050, 

shale 

655 

to 

665, 

gumbo 

2050 

to 

2080, 

boulders 

665 

to 

730, 

clay 

2080 

to 

2105, 

gummy  shale 

730 

to 

760, 

loose  and  gumbo 

2105 

to 

2125, 

gumbo 

760, 

to 

775, 

sand  and  gumbo 

2125 

to 

2155, 

hard  shale 

775 

to 

785, 

gumbo 

2155 

to 

2160, 

sand,  shale 

785 

to 

815, 

sand 

2160 

to 

2165, 

gumbo  —  2165—  8-inch 

815 

to 

825, 

clay 

casing 

825 

to 

860, 

gumbo 

2165 

to 

2365, 

broken  sand    and    shale, 

860 

to 

885, 

sand 

showing    little    gas 

885 

to 

960, 

shale 

2365, 

500   feet   of  oil   stand   in 

960 

to 

965, 

rock 

hole.      Well    bailed    dry. 

965 

to 

970, 

gumbo 

Drilling    commenced    at 

970 

to 

980, 

sand 

2377  sand 

980 

to 

985, 

rock 

2365 

to 

2377, 

sand 

985 

to 

990, 

lime  rock 

2377 

to 

2425, 

sand  and  shale 

990 

to 

1000, 

gumbo 

2425 

to 

2440, 

gumbo 

1000 

to 

1035, 

shale 

2440 

to 

2462, 

shale   and  gumbo    (most 

1035 

to 

1038, 

rock 

shale) 

1038 

to 

1055, 

gumbo 

2462 

to 

2470, 

shale 

1055 

to 

1090, 

shale  and  boulders 

2470 

to 

2475, 

hard  sand 

1090 

to 

1105, 

sand 

2475 

to 

2498, 

gumbo 

1105 

to 

1120, 

gumbo 

2498 

to 

2506, 

gumbo  and  lime 

1120 
1160 

to 

to 

1160, 
1175, 

shale 
gumbo    and   boulders 

•!.r)06 

to 
to 

2524, 
2529, 

tough  gumbo 
soft  shale 

1175 

to 

1195, 

shale 

2529, 

Hard  gas  rock  and  2-in 

1195 

to 

1198, 

rock 

core  taken;  5  3-16  liner 

1198 

to 

1235, 

shale  and  boulders 

was   set.      Well  came   in 

1235 

to 

1238, 

sand   with   streaks    of 

making    dry    gas    after 

gumbo 

bailing 

1238 

to 

1285, 

gumbo 

South   Field,   Nine   Miles  South   of   El   Dorado. 

They  are  still  bringing  in  1,000-barrel  wells  in  the  south  field,  and  there 
is  quite  a  good  deal  of  activity  there  at  present.  Much  of  the  oil  in  the 
south  field  runs  42  and  43  gravity.  This  oil  commands  a  premium. 

There  is  being  produced  at  the  present  time  about  40,000  barrels  of  oil 
per  day  at  a  price  ranging  from  $1.75  to  $2.00  and  $2.10  per  barrel. 


EL  DORADO,  ARK.,  OIL  AND  GAS  FIELD 


— Photo  by  Taylor 
Burning   Well   by   Night — "Arkansas   Lighting   the   World" 


INDEX 


A 

Page 

Acknowledgments 7 

Acreage  and  Oil  Prices 11 

Air  Lifts  for  Raising  Oil 66 

Annona  Tongue,  Austin  Chalk   (?) 81 

Arkadelphia  Clay 80 

Association  of  Oil  and  Water 33 

Analysis  of  Underground  Waters 31 

B 

Blossom   (?)    Sand 81 

Bridges  and  Plugs  of  Cement  or  Other  Impervious  Ma- 
terial   28 

Brownstown  Marl 81 

Bureau  of  Mines,  Co-operation 12 

Busey  Well 8 

C 

Casing  Programs 14 

Cement,   Use  of 34 

Chemical  Analysis  of  Water,  Comparison 31 

Completing  Wells 18 

Conclusion    68 

Constantin  Well 8 

Conservation,  State  Commission,  Regulations,  etc 12 

Counterbalances  and  Tail  Pumps..... 68 

D 

Deeper  Production,  Protection  in  Case  of 43 

Dehydration  of  El  Dorado  Oil , 60 

Drilling   Costs 22 

Drilling    Methods 13 

Drilling  Methods,   Some   Mistakes 79 

E 

Eagle  Ford    (?)    Clay 81 

Equipment    and    Power :..  13 

Evaporation  Loss  of  Crude  Oil 48 

F 

Flow  Oil  Through  Tubing 66 

Fluid  Levels,  Comparisons  of 28 

Formation,  Production  and   Casing  Records ...  26 


G 

Page 

Gasoline  from  Natural  Gas 62 

Gas,   Production   of 51 

Geologic  Structure  in  the  Region 71-85 

Geologic    Structure,    Relation    of    Sequence    of    Wells 

"Going  to  Water" 30 

Geology,  Studies  of  the  Field 71 

H 
History  of  Development S 

I 
Introduction 


L 
Labor  Conditions 


M 

Map,  Methods  Used  in  Construction  of 76 

Marlbrook  Marl,  Source  of  Oil 80 

Midway  Formation,  Showings  of  Oil  and  Gas 80 

N 

Nacatoch  Sand,  Its  Part  in  Production 80 

Nacatoch   Sand,   Elevations 78 

O 

Oil  and  Gas  Above  the  Principal  "Pay"  Sand 75 

Oil,  Character  of 77 

Oil,  Recovery  from  Unconsolidated  Sands 64 

P 

Packers  Used  in  Casing  or  in  Formation 30 

Perforated  Liners  and  Screen  Pipe 65 

Physical  Characteristics  of  Water,  Comparison 27 

Pool,  How  It  Was  Formed 74 

Possible  Extensions  of  the  Field 75 

Possibility    of    Similar   Fields   Elsewhere    in    Southern 

Arkansas 75 

Power  for   Pumping 67 

Producing  Bed,  Description  of 76 

Production  Decline  Curves  for  Oil  Wells 53 

Production,  Estimated  Future  and  Ultimate 53 

Production   Methods 55 

Production    Records 44 

Proven  Acreage 44 

Pumps,  Types  for  Oil  Wells 64 

Q 

Quality  of  Oil ...  48 


Page 
Recommendations    68 

S 

Safety   Devices 56 

Saint  Maurice  Formation 79 

Separations  for  Oil,  Gas  and  Water 58 

Storage  and  Marketing  Facilities 11 

Structure  of  the  Field 71-85 

Surface  Wastage 48 

T 

Testing  Formations 14 

Tracing  Underground  Flow  of  Water  by  Use  of  Dye,  etc.  29 

U 
Underground  Waters,  Analyses  of ; 31 

V 
Vacuum  Pumping 67 

W 

Water,  Amounts  Produced  by  Wells 22-27 

Water  Conditions  22 

Water,  Comparison  of  Physical  Characteristics 27 

Well,  Record  of  Hammond  No.  1 82 

Wells,  Abandonment  of 41 

Well  Spacing 44 

Wilcox  Formation 80 

Y 
Yegua  (?)  Formation ...  79 


The  RALPH  D.  REED  LIBRARY 


DEPARTMENT  OF  GEOLOGY 

UNIVERSITY  of  CALIFORNIA 

LOS  ANGELES,  CALIF. 


THE  LIBRAin 

OflVERSITY  O  (  i.-M 

L0« 


MonofocttHid  bv 
::.j  ©AYLORO  iROS.  | 

Syr.cus.,  N.  Y. 
•          Stockton,  CM. 


UCLA-Geology/Geophysics  Library 

TN872A72B4 


I  III  II  II  I II  Illl  II  I 
AA    001  289  038    o 


